An SD Premium lesson on Bias Voltage

[@TRAXRIPPER]

Bro! THANK YOU SOOO F##KING MUCH FOR NOT JUST THE AMOUNT OF CONTENT YOU PUT OUT BUT THE VALUE OF INFORMATION AND DETAILS AND REASONS WHY AND WHY NOT AND HOW AND HOW NOT.... It would take me a year to actually break down the amount of ways you have taken us there and back. All the positives, all the negatives! When to hit the break or steer around that rack! From the pinions in transfer or replace that case snapped or the rear stripped the gears to drop the tank leak EVAP! When to not lose your head and stay grounded or when to stay neutral so we can remain more well rounded! Sometimes when all else fails and we are stuck in the dark! A back probe a test light an ohmmeter A SPARK! A simple broke relay could be all it takes then she starts! To help us from ripping out all our hair as we stripped it to scrap it and sell it all off for parts cause you have taken the time to help us diagnose all the diagrams code the wires and charts! From tool carts and ratchets and extension attachments with sockets and drivers to wrenches to slip bust a knuckle and crack it! Then take a sledge hammer out back to find something TO LET THAT RAGE OUT AND SMASH IT! Then remember a tip that you slipped in real quick and skate back like from practice and crank off slap shots galore to score the goals for the hat trick! There's a difference from being a fool ass tool with a jack who gets off as a hack who just whacks it away at the parts store all day wasting cash by the stacks then 8 out of 10 times try to bring it right back! To knowing with witt when to hack it legit and look like a boss when you save a fine chick without a rip or a stain on your shirt or jacket! YOU ARE A TRIPLE O.G. WITH THE SNAP ON TO MAC IT! THE SCANNER IS DANNER A WALKING TALKING INFO MECHANICAL PACKET! THATS REAL AND JUST FACTS FOR ANYTHING THAT YOU LACK! LONG AFTER WE'RE GONE THERE IS NO DOUBT THAT THE STATS WILL REFLECT ON MANY GENERATIONS TO COME AND THEY WILL LEARN THE RIGHT WAY TO ACT YOUR GIFT HAS A WARRANTY OF MANY LIFETIMES IMPACT! THATS A WRAP FOR THIS RAP! THE ONLY WAY THAT RIGHT NOW THAT I COULD THINK TO GIVE BACK ALL LOVE FROM TRAXRIPPER WHO STAY ON JUST OUT RIPPIN THE TRAX! Things have been rough for me and things have been tough but I tell you my man on this I go all in with no bluff... I COULD HAVE LIKE TEN LIFETIMES AND STILL FEEL LIKE I LEFT YOU ALL SHORT OFF AND CUT TO THE AMOUNT AND THE WAYS THAT I CAN NEVER THANK YOU ENUFF! ALL LOVE BRO! GREAT F##KIN STUFF! T Ryan Amrhein aka TRAXRIPPER aka Yankster Da Gangster aka Mid West White Boy WHAT UP!

[@ScannerDanner]

Dude I'm crying man. For real, not kidding....no words except I felt that.

[@TRAXRIPPER]

@@ScannerDanner don't worry I can ramble out enough words for me you your brother and son ten of your friends and the last 6 graduation classes! Lmao if I was a fish I'd be a large mouth bass hole! A record setter for how many times I been thrown back cause I don't shut the hell up! Ha ha ha ha!

[@pitchforkpeasant6219]

Damn. That’s saying something 👍😁👍

[@alexdbr193]

Paul is my mentor!!! I’ve been watching all of his vids and reading his ebook, has helped me a lot as a new tech

[@ScannerDanner]

Thank you!

[@ScannerDanner]

The two people that thumbs downed this video so far must like to use their ohmmeters for circuit integrity testing lol

[@SuperSecretSquirell]

Our electrical troubleshooting instructor warned us that he'd smack us if we answered a circuit integrity problem with "continuity test" lol.

[@TheWCleveland]

Dynamic testing is the future

[@JimmyShagoury]

Lol I’d hate to meet a person who would dislike a scannerdanner video.. must be super annoying honestly 😂

[@ryan8488]

They are parts changers

[@frankjohn4302]

Right you are Danner

[@nickyborrisino]

It is always a pleasure to listen to someone when they genuinely enjoy what they do.

[@JaredHIll13]

9:20 I can vouch for this personally guys... listen to SD here, espically if u want to be a good tech. I was made fun of at my old job for doing "stupid extra tests" before i would finish my diag and request parts. Funny thing is... Within 1 year i had surpassed the electrical diag ability of everyone in that shop, some 20 year veteran parts changers lol.. AND the learning never stops. It helps me stay motivated and is rewarding, if u can save a customer money yet still make good money on ONE correct repair. Remember guys were in the trenches as auto techs and can have a massive affect on peoples lives.. for the better or worse.

[@timothybarnes533]

I can attest to the faster learning curve by being in Scanner Danners classes.I think I've only been in his class for 10-1 year.But, when I first started as a Mechanic and I mean a Mechanic I was turned into a Assistant Service Manager for a company called Monroe Muffler.Where I diagnosed and made repairs on new and old cars and trucks.(Gasoline and Deisel)And stayed turning wrenches and studying Danners classes online.I lean towards the Electrical Automotive side of things because it's helped me move up as Technician.I just hit play and let Scanners drill it in my head.It works I promise

[@alb12345672]

@@timothybarnes533 I have an electrical engineering degree and this concept is burnt into you. We focus on the design side of things though, and that can get complex when parameters, cost and reliability gets involved. It is also the basis for what is a modern computer. WIth circuits (and logically combining the results) you can do arithmetic, compare numbers, etc. Pretty much the processor in your computer. Probably way overkill to work on a car, but I have a sense for almost any electrical issue.

[@rockynix7731]

@@alb12345672 sounds like to me you have a disfuction Way of thinking dude .... I think you're Brain is mathematically confused .

[@gnomiefirst9201]

@FiveTwoMoto: Herd mentality to make fun of or ridicule the things you don't understand.

[@medch4193]

i love the way you treat your son you are such a good father

[@xrxgustavoxrx]

Thanks I'm from Bolivia and this explains a lot of things and save time and money in a diagnostic field, I barely speak English but I can understand every single thing that you say sorry if I can't express correctly. Gracias teacher paul!

[@slavcata]

Hi Paul and Caleb. Been a subscriber of the SD Premium for an year and a half . For £9 per month there is no other place where you can gain knowledge in that volume. Bias voltage is another proof of that you need to sit on your bottom and just watch the lectures . What a eye opener !!!THANK YOU . Keep up with the great work. God bless!

[@ScannerDanner]

Thank you so much Stan!

[@ColeTanner88]

Great point you made in the video! You can sit in class all day and "know" something. But until you're in the field and your paycheck depends on making the right call, it wont fully sink in as far as voltage readings, voltage drop testing, etc. Ive seen it multiple times with techs coming out of tech school. We never forget those bad calls and we hopefully wont make them again, IF, we take the time to understand why/how we made the bad call in the first place. This stuff really does come "alive" and will give you a "lightbulb" moment, if you're in the field and going through these teachings/testing procedures. Understanding the fundamentals can take us farther than most. Even if we've been in the field for years, going through these teachings again, we can pick up on things that were overlooked or hadnt sunk in yet.

[@ColeTanner88]

I also remember the case study on that Ford you're talking about in the video. I was just talking to a coworker about it the other day. I couldn't remember where it was coming from/why, but remembered the 29v or whatever. Great explanations here, I use bias voltage checks regularly. Haven't ran across one that will light a test light yet, so I'll have to remember that variable. Funny how we think something is an "absolute" and then see something that contradicts our thought processes and experience. I try not to say always, never, etc when teaching other techs.

[@ScannerDanner]

Did I mention the bias that lit a test light? I actually was able to prove that was a bad test and there was another variable to it! I have that lesson recorded as well.

[@ColeTanner88]

@@ScannerDanner I'll have to check that out, I don't recall watching that one yet. Did you put a link to it in the video? If you did, sorry I missed it.

[@ScannerDanner]

​@williamtanner8222 I believe it is in this series.. This is from the description: This is a clip from a 5 part series we recently completed on ScannerDanner Premium titled "Circuit ID and Integrity Testing (2020 Edition)" To watch the rest of this class, sign up for the 14 day free trial we offer right here www.scannerdanner.com/join-scannerdanner-premium.html Thank you and I hope to see you there!

[@ColeTanner88]

@ScannerDanner okay, cool. My boss pays for premium(h-tek auto care). I'll check it out. I know its confusing, williamtanner8222, I aways "sign" my comments Cole, on your website. William Tanner is my "gov-ment" name, I go by Cole🤣 you interact with so many ppl, you probably won't remember and that's okay, I won't take it personally

[@steamy1225]

Wow. That was great . I worked on cars before and still do on my own cars only but never heard of Bias voltage. I would call it residual voltage. But great explanation on bias voltage. Learned something new today. Thanks Scanner Danner.

[@josedejesusvelazquez6863]

incredible video Paul well explained and ecxelentemene executed. May God continue to give you that intelligence and receive many blessings. Greetings from Tijuana 🇲🇽 Mexico.

[@ScannerDanner]

Thank you my brother

[@MoparMadness93]

Danner just got your book! Thanks for all the effort you put into your material as well as the videos! They really show where your hearts at and what kind of man you are!

[@ScannerDanner]

Thank you so much

[@MoparMadness93]

@@ScannerDanner just know your doing good in this world set on everything bad

[@ScannerDanner]

🤗

[@AutoDiagnosticsPK]

13:27 - i am not a mean father.... Surely you are not!!!!! You are a good teacher, a human being and a good family man Paul... Stay blessed and love you❤❤❤❤

[@ScannerDanner]

thank you sir

[@erikkirby1]

Lerned about bias voltage three years ago by you Dr D! have been a subsciber to premium ever since!!! God bless you!!!

[@ScannerDanner]

Oh wow thanks so much! You've been with me for a long time! I really appreciate guys like you, as I'm sure you've watched every video I have by now, yet still choose to support me for the content I'm providing both here on YT and on my premium channel. I can't thank you enough.

[@erikkirby1]

@@ScannerDanner It's always a good refresh to revisit your videos!

[@JimmyMakingitwork]

Great class! Sometimes I’ll use my wire spool to bring battery power and ground with me to the diag area. So many issues with poor connections causing wasted time!

[@armandonika]

I have become lets say “good” at this Paul and MAINLY is from you man! Thank you very much Professor 👨‍🏫

[@ScannerDanner]

Thanks so much!

[@alexlimo6959]

I admire how you teach us ,from kenya....

[@ScannerDanner]

I appreciate that. Thank you!

[@metall111]

ScannerDanner is best of the best. Thanks for sharing this.

[@spelunkerd]

I don't remember if I saw this one before, but a 👍from me wasn't showing on my computer, so I watched it again. There's something compelling about understanding how the PCM knows enough to set a trouble code. There are all kinds of clever design features in vehicles that are hidden from view, only discovered by those with the curiosity and insight to ask themselves why the finding is there.

[@johnmckamy6398]

Your a legendary teacher .

[@ScannerDanner]

Thank you John

[@fmbfla]

My congratulations to all your students graduating and to you Danner for teaching the new.

[@davidblaze1652]

I would definetly check this video with that 29 volts fuse. Love when parts canon is been fired and SD fix it within 10 min. 👍

[@alanw5879]

I think about that video alot, that one reminds me all the time almost anything is possible and once you understand whats causing something like 29volts, it helps get your thinking straight.

[@davyarthurs]

As soon as you showed that rusty weld, I thought I remember this case study from all those years back!

[@MegaRyad]

this was a very frustrating subject for me , i seen it on your other videos but did not understand it , but this video is gold , i understand now , thank you very much

[@windward2818]

From experience I can tell you that Detroit auto OEMs development and engineering staff, which includes all of the shop technicians (auto mechanics) are DMM centric when it comes to general troubleshooting (looking at all circuit types, 12VDC, 5VDC, 2.5VDC, without the worry of damaging the DMM due to very high input voltage, e.g. Fluke 87V goes to 1000V, where most ignition coil primary voltages are clamped at around 430V, just in case you encounter high voltage), where the most popular brand is Fluke (for many reasons like; yearly calibration consistency, OEM testing experience (ruggedness), input protection, etc. e.g. Fluke 87V). If the electrical engineers and technicians want to load a circuit they can just use a large non-inductive +/-1% Tolerance power resistor at an appropriate value to load the circuit. You usually only need 4 or 5 large power resistors to cover all testing in a passenger car or light truck. These are custom made with silicone leads and stacking banana jacks (you can choose either shrouded or unshrouded depending on what lead sets you use), the DMM is set to VDC and the test resistor plugged into it with the normal test leads plugged into the resistor stacking jacks. So why use a DMM + resistor to test a circuit with a load rather than an incandescent bulb or a 12V test light? Many reasons: 1) You know more about the circuit under test. For a simple example. I want to test a 12VDC power feed but under a 1.2 Amp load. According to Ohm's law my load resistor would be 10 Ohms. When I take my voltage measurement, let's say it is a little low at 11VDC, I also know the amount of current being drawn by knowing the resistor value and Ohm's law; 10 Ohm resistor, Current = 11VDC/10 Ohms = 1.1 Amps. With the DMM I know the circuit voltage and my test load current very accurately. 2) Incandescent bulbs have a cold current inrush current which is 10 to 15 times its fully hot current, with a 1 Amp bulb you can easily draw 10 amps, which is why bulb testers burn small PCB traces. Non inductive power resistors as a load do not have a momentary inrush. 3) Incandescent bulbs are made of glass and can break. 4) Incandescent bulbs burn out. Planar chassis mount power resistors last decades. 5) Incandescent bulbs when hot can burn you or the car (like carpeting). With a power resistor you will dissipate energy (make heat) but there are several ways of dealing with this. The most popular is to mount the resistor to a small aluminum heat sink with fins and cover with large heat shrink keeping the ends open for air flow. This works good because you hardly every have the load present for more than a minute. The heat shrink will keep you resistor and heatsink from shorting across something. 6) If I want to load a PCM 5VDC reference output I can choose the best resistor to load the circuit. So if I want to load it at 250 mA I would use my DMM and a 20 Ohm resistor (I use a 22 Ohm which is a common value available). 7) You can use a load resistor to eliminate 12VDC ghost voltage when measuring power feeds due to the very high input impedance of the DMM on DCV. If I load the circuit with 100 Ohm resistor for 12VDC testing I will draw 120 mA at 12 Volts DC which will defeat any ghost voltage. I am essentially decreasing my DMM input impedance (resistance) by adding a resistor. Now for the bad news. All of the above costs money. In Detroit you have to pay to play. I don't think I have ever seen a single incandescent bulb used as a tester or a test light which was not LED at an OEM testing garage or tier one supplier, and then the LED test light was used only for simple 12V lighting circuits. You just learn to use your DMM for everything until you need to use a scope, if you need a load, add a load. I have made some special purpose gadgets for testing either LED based or 12V buzzer based, but these are usually done at the request of the lead garage technician, or a project engineer. For an intermittent 12VDC power feed a buzzer is really handy. You can wire in the buzzer and then move the harness until the sound is interrupted. You want to pick a buzzer that is quick responding. A Fluke 87V is very powerful if you know how to use all of its features; like Min, Max, Relative resistance reading, accurate low current readings, true RMS on AC, etc. Popular resistive load values for automotive 12V systems: 6.8 Ohm, 10 Ohm, 22 Ohm, 100 Ohm, and 1000 Ohm. In closing I think we should ask ourselves why certain incandescent bulb testers are used per the different currents drawn at steady state. Many users of bulbs will use a 1 Amp bulb or a 4 Amp bulb, but, other than they are readily available in these standard sizes, it would be good to know why the user thinks that particular current draw is of significance. So, the questions is why are you using a 4 amp bulb as opposed to a 1 Amp bulb? What do you think the 4 Amp bulb will do for you? Why don't you just directly emulate the needed load with a resistor?

[@anthonysova7117]

Very good vid I found myself answering your questions without guessing because of your book that feels good knowledge is power Thanks for sharing your knowledge Cheers by the way I used your book recently to prove a point about thermistors to my buddy

[@ScannerDanner]

Excellent! Thank you so much my friend.

[@chubbychequer1512]

Where do I buy the book

[@fascistpedant758]

I searched for "ugly" and Scotty Kilmer came up!

[@johneric3886]

Wow the misplace fuse caused all those problems..... That one hurt me and it's not even my car!!! Hope you and your brother are well scannerdanner, know I think highly of you both. _____I think because I was raised in Ohio I have many of the similar behavioral characteristics of you and your brother, and yes that is a good thing as far as I'm concerned!!!

[@nickayivor8432]

Good Morning ScannerDanner 🙏 🌄 Take care and have a great 👍 👌 🌟🌟🌟🌟🌟 Great tutorial thank you 👍 ❤ it. From Nick Ayivor from London England UK 🇬🇧

[@Sagittarius-88]

Many years ago, I built myself a set of 20 foot jumper leads out of radio shack mega-cable. I'm sure a lot of youngsters are probably asking themselves "wtf is radio shack mega-cable?" but I digress. You just had to be there. My point being, I can attach to the battery, and take hot and ground with me anywhere in the vehicle without wondering "am I on a good ground?". Yes, I understand there's certain instances where being attached to body or chassis ground is better for particular testing. However, the vast majority of the time, being solidly connected to battery ground is fine for testing. Removes a lot of the guesswork.

[@aaronrepsher7628]

The whole intro of the video about testing with a "unknown" ground thats all I'm thinking of is my retractable dual lead set and I do the same as you sir!

[@JamesBacarisas]

Thank you so much Sir Scanner

[@workwillfreeyou]

A 15' long meter lead that could go directly to the battery negative post could be cheap and helpful.

[@kenmelrose3429]

EVAP NOOOOoooo ... We know how Paul likes to do EVAP testing

[@throttlebottle5906]

we should contrive a way to send him 20 evap. issue vehicles in a row! I'm sure he'll love this comment :))

[@triggera3851]

Hahaha shine the flashlight here!!! My dad did the same and eventually I figured out why hahaha. That's the first thing I thought about when you were talking about the cameraman thing lol.

[@alb12345672]

This is just like my electrical engineering class, but we had to design for various parameters. There are also other configurations too, where it can become an amplifier. That circuit is also the basis for 90% of the stuff that goes in computers and microprocessors. Once you can "NOT" "AND" and "OR" those things on a scale of a billion you have a modern processor.

[@nancylewis7142]

Thanks for this video Paul.

[@ScannerDanner]

Very welcome

[@IAMNOSLEEP]

Thanks for sharing Paul... Cheers.

[@isalmankhan1]

Great lecture on Bias voltage⚡ Thanks for sharing SD👍 Special thanks to Caleb😉 Stay Safe Guy's❤

[@ScannerDanner]

Our pleasure!

[@Jimmy.meyer.76]

That was awesome. Great info and case study. Thank you .

[@paulfiebke3909]

Keep up the good work and God bless

[@martinrubenstein7943]

Paul, you said that the observed 2.9V bias voltage was quite possibly a 5V bias source being dragged down to 2.9V by the finite impedance of your meter. You then said that for all we know, the bias voltage source might even be 12V through a very high bias resistor, that the meter is then dragging down to 2,9V. Could I offer a thought why it’s probably not a 12V bias source? In one of your early lectures you explain that bias voltages are there to allow the ECU to check for circuit integrity. In this case study, the fuse was blown, so you had 12V on one side of it and 2.9V on the other side (let’s say the ECU would read a true 5V without the meter in place).. The ECU would then see 5V instead of the 12V it expects to see on a normal circuit. So the ECU would then know there is a break in the power supply circuit and would flag a fault code. But if the designers had used a bias voltage of 12V, the ECU would see 12V even when the fuse was blown, so that would be of no use as a circuit-integrity monitor; the bias voltage has to be significantly different to 12V eg 5V if it’s to be of use as a diagnostic tool. Would you agree with my thinking? (By the way, another superb video showing bias voltages in practice.) N.B. I do understand the point you’re making - why you said the bias voltage might even be 12V: you were pointing out that bias circuity is, almost by definition, there to inject a ‘weak’ voltage into the circuit for the purpose of onboard diagnostics, and the very high resistance in bias circuitry is so high that even the high input impedance of a meter is enough to load the circuit and dramatically drag down the true voltage, giving a lower and false, measurement

[@priyamshah50]

Had fun learning!!

[@jorgegonzalez-bk8zn]

One good one that happen to me 2011 ford ranger timing job crankshaft sprocket slightly different due to aftermarket parts on wrong box got the sprocket for a engine with balance shaft and the harmonic balancer when in a couple mm further in and crankshaft sensor had a intermittent signal

[@ScannerDanner]

The video i mentioned with the 29v? That was one of the issues with that vehicle too! And is why it got the parts shotgun lol, crazy stuff for sure. Thanks for sharing!

[@michaelkennedy2528]

@scanner danner hey, I have have EVERYTHING rotational checked on that 2000 Ford Windstar with the rough Idle. All within specs.

[@ScannerDanner]

I cannot help you with this one my friend, sorry.

[@donniejohnson7499]

Awesome video!!!!

[@danjensen100]

best teacher ever, seriously. I owe so much of my success to you Paul! Edit to ask: If the car wasn't starting, why was it pulsing the trans solenoid (which caused the 29v back feed). Also, even if the fuse is in and the car is in working order (like the newer one that you compared the voltages to, to confirm your theory) wouldn't that 29v back feed cause problems with the system? Thanks, Dan

[@ScannerDanner]

Half the PCM was alive and the other half wasn't is the only explanation I can give you. Thank you Dan!

[@mikesabin8568]

Run a power probe to the point your testing. The alligator clip is a good ground so use that clip as a known good ground for testing and there is never any a question.

[@ScannerDanner]

Just don't expect to see a bias voltage on any circuit if you are measuring voltage with the PP, it will pull it down. The internal impedance is very low compared to a typical digital voltmeter. Good tip on the ground connection of the PP, I use it all the time!

[@chekelley6861]

@@ScannerDanner I think he was saying to use the PP as a known good battery ground.

[@ThatEEguy2818]

About the voltage behind that diode supplying the bias voltage in the example of 2.9V, it's my educated guess that the supply voltage is around 3V or 3.3V. It's possible that the diode isn't there and the supply is 12V, but that wouldn't really tell the computer anything through the sense circuit besides a shorted/open driver. If the bias is low and the diode is present, the computer can distinguish an open coil circuit and a shorted/open drive circuit.

[@canadatransistor]

Paul, you should try troubleshooting with a digital probe. By concept it's similar to a test light except it follows transistor - transistor logic. Benefits include you can identify if the circuit is pulsing (whereas sometimes pwm is involved but the naked eye can't tell the duty cycle) it can tell you if you are at logic HIGH and logic LOW such as the ability to sink or source current. (similar to pull up or pull down circuits) Seriously, give it a try, they are not really expensive and it's an easy learning curve. I have a feeling GM may be employing stuff like this in their tech's training and equipment. Cheers bro, Louis

[@tonyp.autorepair994]

Thanks for you valuable support 👌👌👈👈🙌

[@Joeelectronicschematicsforauto]

You are a legend

[@James-id5xq]

Should I have a $3500 remanufactured transmission (jasper 100k warranty) put in an 03 Lincoln Town Car with 180k? I love the car and its otherwise in great condition (engine, paint, body, suspension, interior). I drive 60k highway miles a year for work and diy all the maintenance/repairs. Plastic intake manifold already replaced lol damn 2v 4.6

[@ScannerDanner]

tough pill to swallow, how about a used one? Have you looked?

[@James-id5xq]

@@ScannerDanner 2 shops quoted around $2000 parts and labor for used. That is with fluid and a new cooler. I believe the engine will last another 100k highway miles because it runs like a Rolex and only burns 1/2 qt of oil ever 5k

[@UnlessRoundIsFunny]

Yes, you absolutely should, provided the body and interior are in good shape. I've got a 2003 Grand Marquis w 200k miles and the original transmission, and the car is mostly bulletproof and, when it breaks, it is dirt cheap to fix. The only big ticket item between now and 400k miles is a transmission, and I will gladly buy one when the time comes. You can't buy a town car with less than 100k miles right now for under 10 grand, and even older ones with 200k miles are going for 5-6 grand. $3500 to hang on to a model in good shape, with a 100k mile warranty on the transmission, seems like a no brainer.

[@ThatEEguy2818]

Just something to add about the coils magnetic field causing that voltage spike. The magnetic field of an inductor, or coil, wants to keep current steady. It opposes change in current. So, when the switch is first closed, the current begins to ramp up. If the inductance is constant and the applied voltage is constant, then the ramp up of current is constant. For the real techies out there, this is true until the core material of the coil saturates with magnetic flux and/or the wire resistance comes into play. The point of this post is, the collapsing magnetic field doesn't directly cause the voltage spike. The collapsing magnetic field wants to keep that current flowing and essentially slams it into the open switch contact in an attempt to keep it flowing. This slamming of current is where the back emf comes from. Think water hammer in plumbing. Anyway, the back emf will rise to a voltage required to stop that current, or it'll blow over the switch contact. A third option, and this is usually what's done in reality, is the circuit is designed to allow the back emf to rise to a limited voltage before it allow the current to continue to flow, thus holding at that back emf voltage. The high back emf voltage pushes back on the current bringing it to a stop, then the back emf is no more. The higher the back emf, the faster the current stops. A side note, the back emf may not be gone when the current stops due to parasitic capacitance, which can cause the circuit to ring (oscillate) a bit before it settles down.

[@gnomiefirst9201]

I have been wondering about the reverse voltage EMF induction spike bc I have read that the backfeed induction spike could cause computer circuit damage e.g. not giving spark plug a ground path when doing a kill cylinder test. I was pooh poohed by a mechanic friend re this bc he has never had any untoward result from doing so. Do the engineers design stuff to be able to handle a loss of ground? Thank you.

[@ThatEEguy2818]

@@gnomiefirst9201 there is some danger in running a spark plug without a ground as the spark voltage will rise until it blows over somewhere. That somewhere may be inside the coil itself, which can damage the coil. I doubt that protection against this has been incorporated beyond another spark gap that's much bigger than the plug but small enough to protect the coil. I'm speculating, as I know no details about how the coils are designed. They seem to be able to survive a little while open circuited but I don't think they're guaranteed to.

[@gnomiefirst9201]

@@ThatEEguy2818 thank you for your reply.

[@Pablo_Automotive]

Thanks a lot for another great explanatión about circuit testing.

[@ScannerDanner]

Thanks for watching Pablo!

[@MarioDallaRiva]

The Danners ARE the MANners! No bias here 😝😎

[@ScannerDanner]

🤣

[@CharlesLease-ei1ee]

Talking about grounds if you worried about a ground, just go directly to the battery and you don’t have to worry about it

[@ScannerDanner]

100% but in my case I was in the back of the car without a 15ft jumper wire to get me there.

[@ingejeppesen1358]

The sense feed voltage can't be 12 volts, because then it wouldn't be able to set low voltage codes with an open curcuit. I would say it uses the 5 or 3.3 v regulator inside of the pcm.

[@michaeldecker8853]

12v on power wire 2.9v on control ground wire for Nissan rogue intake and exhaust control solenoid valves while harness was unplugged from solenoid.

[@ScannerDanner]

Sounds like a good circuit

[@صلاحالحراصي-غ1ض]

28:09 you scarred me Mr. Paul 😅

[@ScannerDanner]

lol

[@aldosaldana3445]

Amazing content as always. 21 yr old beginning to step foot into the advanced diagnostics world. Currently reading your book, & subscribing to your sd premium by the end of this week. Quick question, as far as circuit integrity testing, will a digital display circuit tester prove good or bad circuit the same way a classic bulb style circuit tester will?

[@marvinnaputi7867]

Scannerdan I am try to learn more about electrical diagnosing how can I get your book or sign up to your classes on line.

[@ScannerDanner]

www.scannerdanner.com/join-scannerdanner-premium.html Thank you! Look forward to seeing you there. If you have any difficulty signing up, email us at [e-mail]

[@drivewasher]

If the ecm monitors the ground side wire for voltage, IE to see if circuit is on or off. Then why would it use a bias voltage as well? Is that how it knows it's short to ground rather than just switched on. Does this question make sense?

[@ScannerDanner]

Good question! Here is the tricky part in answering this question. Pick another GM, maybe even the same year and the same circuit, and there is no bias there at all! So why on one model and not the other? These circuits are built for diagnostic purposes, no doubt, but I've also read some literature on analog to digital converters where a bias line is used to aid in that conversion process, so who knows. In this case though, we could argue that the ECM can now determine the difference between an open and a short to ground. No bias, the ECM would see 0v in either case. with a bias the ECM will see 0 volts with a short to ground, and some voltage off zero for an open. Make sense?

[@ralfsautomotive]

As usual Spot on!

[@speedy_pit_stop]

Awesome. Expect the unexpected. Good video.

[@bryanlamontagne2914]

Hey Paul, this video got me to thinking why the manufacturer flow charts don't have you measure the bias voltage, because on your meter, say for example in this video, you would read 2.9 volts where my meter might read 3.4 volts, and someone else might get a reading of 2.3 volts, depending on the internal resistance of the meter. Of course, they could always say to measure making sure you used a 10 meg ohm impedance meter. Just a thought.

[@ScannerDanner]

they really should! I don't know why they don't? Instead they want you to dig the computer out of wherever it lives, disconnect it, then disconnect the output device, then use your ohmmeter to check for opens and shorts. smh A bias voltage test is 1000 times faster right?

[@bryanlamontagne2914]

@@ScannerDanner For sure!

[@85jmccoy]

@@ScannerDanner danner i went to u.t.i. and graduated in 08,they taught us good electrical classes but i still wasn't 100 percent sure what i was doing,then i got in a dealer and started gettin my feet wet in diagnostics and used the flow charts.....and i never understood why they had me unplugging computers and devices to Check circuit integrity. Then i found your videos and bought your book and i took off man you give people so much confidence and explain things that are easily understand. Thank you sir!

[@ScannerDanner]

@@85jmccoy thank you so much my friend

[@m.b.smoshitoa8325]

hi paul i heard you in most videos talking about bias voltage but did not understant what is it . it is only today that i understood it. according to my understanding bias voltage is just a voltage disigned to confuse technicians. it has no use other than than. your 2 years follower m.b.s moshitoa (south africa)

[@ScannerDanner]

I use it to determine circuit integrity. I has a HUGE advantage for a tech when you understand how to use it. 😉

[@victorgonza4528]

That was really good thank you .

[@4dirt2racer0]

hOly shit! thank u sooo much for providing these for free brother!!!!! dam i cant thank u enough!!

[@kenmoore800]

Paul you said you had the 2.9 bias voltage all the way back to the blown fuse,was that before or after you cleared the short to ground near the door I assume after because the short would pull your bias to 0 and the remainder of the circuit from the short to the fuse would be at 0 volts?

[@ScannerDanner]

The short to ground was intermittent! Great question! It was not shorted when I was doing those checks

[@superbestdad]

Circuits like these are why we have big foreheads. Scratching your head and sliding glasses on and off tends to plow the field. I took a little mental field trip on an early 2000s ford ranger that I’ll never forget. With main PCM fuse pulled and KOEO probing both terminals, supply 12...PCM “load” side 24VDC. It’s the kind of thing you can’t just go look up lol. Interesting way of protecting the PCM. I had already found and fixed electrical problem but then noticed that KOER my PCM supply was less than charging system voltage. You can pay to go to a class and hope they teach you everything you need to know in the field or you can take the basics you’ve learned and figure it out. Either way cost you money but I’ve done both and the lesson sticks better when it kicks your butt, you touched on that in this video. Good stuff man. On an edit: I typed this comment before end of video, as soon as I clicked play you go into blown ford fuses lol. My thinking was that Ford was by design creating the higher voltage from a transformer in a means to protect the board. That critical 16-18 “poof” range wouldn’t matter

[@MarioDallaRiva]

Paul, I’m watching the 29V SD Premium videos…Holy Carp, that car needs an exorcism!! Thankfully St. Paul is there to exorcise the demons! Fascinating content. SD Premium is the cat’s left nut, as we say 😼👍🏻👏🏻

[@triggera3851]

Awesome information

[@ScannerDanner]

Glad you think so!

[@Joeelectronicschematicsforauto]

It's really almost the same circuit just flip-flopped transistors being used as a switcher not an amplifier through the collector emitter when it gets saturated it's a switch and then the voltage is on the solenoid 12 volts they just rearrange the solenoid and transistor I am assuming transistory's npn and forward bias is being applied by a computer to base emitter

[@richardstockwell4862]

I really want to join danner premium i love your channel when i am able to afford this i will certainly be purchasing your book. I would love to get a job with you guys i live one state over

[@gnomiefirst9201]

Another great Vid Paul. I have been wondering about the reverse voltage EMF induction spike bc I have read that the backfeed induction spike could cause computer circuit damage e.g. not giving spark plug a ground path when doing a kill cylinder test. I was pooh poohed by a mechanic friend re this bc he has never had any untoward result from doing so. Do the engineers design stuff to be able to handle a loss of ground? Thank you.

[@nandanalal5072]

Thanks dan

[@ScannerDanner]

It's Paul, Danner is my last name 🙂

[@aleskyfinis1025]

Good video

[@1mrsleepy1]

Dude that welding hack job tho!!!

[@ScannerDanner]

Right? Crazy stuff

[@ralfsautomotive]

Let Needle nose Vice Grips be your friend much better than any alligator clip and once grounded it is there to stay. Just saying, I always seem to have trouble with aby clamps on body parts.

[@richardtrowell8812]

The question I have is why and how would you relocate a fuse. By doing so wouldn't you be creating a problem to diagnose something in future? For someone else.

[@ScannerDanner]

The why and how I cannot answer, but somewhere along the way of this truck being a no start, that fuse was relocated into the wrong spot. Then from there it became an absolute nightmare for many different techs

[@fredsanchez311]

Hi I am a fan and watch your videos. I Do have a situation and hoping I get some direction. I have a question on 2004 suzuki that cranks but not start , and no comm issue and but have proper ground and power on pins 4,6 , and 16 on the DLC . Also ECU is not grounding the control wire on the fuel pum relay control wire, therefore no power on fuel pump. However, I noticed igintion fuse that power fuel pump also powers the ecu and the spark plugs, that wire if I cut it from the fuse now the cut wire stilled attached to ecu shows ground. with a light test This supposed to be power but shows ground when disconned from the fuse does this mean there is a short in the ECU? Also the ECU is not grounding the control wire for fuel pump relay as I said. Would you say the ECU is shorted?

[@AutoDiagnosticsPK]

did i miss the part where purpose of the bias voltage has been explained??? Can someone give me time stamp for that

[@ScannerDanner]

It is for open and short circuit diagnostics. Fault recognition

[@aranhaydar9195]

That laugh at 33:55 🤣

[@TheMasterHackUS]

If a system has bias voltage, will that be spelled out in service info? How would I know outside of just using a test light or loading a circuit instead of a meter?

[@ScannerDanner]

No sir, you will find NOTHING in service info about these types of circuits.

[@TheMasterHackUS]

@@ScannerDanner outside of experience, is there any way of confirming you have a biased voltage? Just experience? I can see where this would confuse and send someone on a wild goose chase if you don’t know.

[@cwj9202]

At around 26 minutes, what caused the fuse to blow that measured 12/29V?

[@ScannerDanner]

Are you talking about the 29v case study i mentioned? The fuse got relocated to the wrong spot in the fuse box

[@V_Vladimir_V]

В последнее время хорошую массу трудно в машинах искать

[@UcantBeSerious03]

13:32 'When you didnt hold the flashlight right and dads already six bottles of angry juice deep and he starts using no no words'

[@ibragimgurbanismailov9090]

at the 23rd minute of this video, you said that you had connected an incandescent lamp, and at the end of the video you said that the incandescent lamp would not light up due to too high resistance. my question is do I need to connect an incandescent lamp or not?

[@ScannerDanner]

Depends what you're trying to do

[@wg8005]

I'm driving a 1998 Toyota Avalon and wondered if they use biased voltage in O2 sensors? I replaced bank 1 sensor 1 and it's running good now. I ran some tests on my battery today and I'm at 12.8 with then car off and 14.1 running which is almost perfect compared to 11.8 and 13.1 before I replaced the sensor. It had problems driving in the rain, used to turn off. I cleaned the maf sensor, idle one and cleaned the throttle body out. Before I did any of this I would try to charge my phone and the car would steal my phone's battery somehow. Any thoughts on O2 sensors and battery?

[@ScannerDanner]

Not sure offhand, I'm sorry.

[@nolmarserolf8313]

Good day sir I have concern to my Toyota Yaris 2015 .the technician checked by computer scanner the trouble code he got is p1603 ,p1604 and p1605. Can u help me to solve this problem.

[@yaseenhashim8538]

thanks awesome

[@mikejmardis]

couldn't the short to ground be cutting the bias voltage from 5 or 12 vlt's to 2.9 vlts because it's a crappy ground?

[@ScannerDanner]

No sir, the short to ground was on the power side of the circuit

[@rpmpamintuan7338]

😅 yess i read 2 wires of 29volts in tps. I am shocked that the tps is still totally fine 😂.

[@brianberggren846]

9:54 in. should be a mantra to avoid. Customers will catch on and find another shop.

[@tnamen1307]

one thing i would like to know .... 1. At time 20.47, 12 v comes down all the way down to the leg of the sensing circuit, and meanwhile, 2.9 v should come through diode and also meet at the same leg of the sensing circuit. 2. You did not mention how 2.9 v behaves through diode and resistance??? If 12 v can come to the leg of the sensing circuit, where is the 2.9 v???? Is it 12 v-2.9 v=9.1 v be the reading at the leg of the sensing circuit??? Please clarify this. 3. How the 2.9 v behaves?

[@ScannerDanner]

there may not even be a diode if the bias circuit is 12v but let's entertain that the source is 2.9 and that there is a diode. I placed the diode there in my imaginary drawing to show the 12v will not be able to backfeed into the lower voltage circuit, that is all. On a good working circuit (no opens), with the circuit off, you will have 12v sitting on one side of that diode and 2.9v sitting on the other side. No current will flow because of the diode preventing the 12v from "flooding" the 2.9 volt circuit. And looking at it from the other direction, the 2.9 volts cannot flow into the 12v circuit because the potential is too high. The sensing circuit will see 12v, with the circuit off. With the circuit on, it will see 0v. The purpose of the bias is for the module to be able to recognize the difference between an open or a short. Without the bias, it would not.

[@tnamen1307]

@@ScannerDanner okay thanks for the explanation. I now know why 2.9 v doesn't flow on the other end of the diode. I have to apply the rule 'current always flow from higher potential to lower potential'

[@PhillyDee215]

Gotta love these evap systems🙄🤣

[@jimmacris615]

Power probe ground

[@ianferguson1281]

I need a good diagnostician. Do you have any former students that operate in Maryland? I live just north of Baltimore and I'll drive far if needed to get to their shop. Thank you

[@ScannerDanner]

I'm sure I do. Are you on FB? That would be the best way for me to find you a tech who follows me.

[@ianferguson1281]

@@ScannerDanner Yes sir. Ian Ferguson. I have a picture of "Yellow Beard" as my profile pic

[@ScannerDanner]

Write up a post and tag me. Include year, make and model and what work you need to have done. I'll then share it

[@brucegill4218]

Hey Paul it's me Bruce I want to tell you about this one probe it's called sigma probe you should check it out it's pretty neat I think you would like it all right you have a nice day I'll talk to you later

[@slickrick343]

That welding. The shame....