Mastering Diagnostics #13: Voltage Drop- The circuit stress test

NOTE: The last of the video has glitched and I wish to summarize here. With a failed fuel pump there is no way to verify the circuit is healthy until it functions. A normally functioning pump will spin as designed and produce counter voltage. A slow pump will not produce the counter voltage and can suffer damage to the brushes/commutator from current flow/heat. That would typically mean the pump would need to be replaced before retesting can commence. If not, the new pump will suffer.
However, substituting a similar current load will stress the circuit and flush the fault to the surface. this will allow you to find the underlying fault before replacing the pump, in this case. the prevents comebacks from occurring.
Motor Age Technical Editor, Brandon Steckler is back again for Mastering Diagnostics in episode number 13. In this episode, Brandon discusses the importance of stress testing the circuit of an inoperative component before committing to the actual repair.
In many situations, a vehicle will present with an inoperative component (like a fuel pump, for example). Many technicians find that the fuel pump's internal circuity is electrically open or has extremely high internal resistance.
As a result, the faulty fuel pump is replaced but the technician discovers (only after replacement) that the circuit still doesn’t function. And here is where the technician went wrong. An open fuel pump will not allow current to flow (and that is the reason for replacement) however, there would be no way to detect an underlying circuit issue (like a poor ground connection or poor contact in a relay).
It's never a great situation when we as technicians or service advisors must face the customer a second time, and in this case, tell them that the $400 fuel pump we had just condemned and replaced still has not corrected the issue.
Follow Brandon through this valuable lesson on Ohm’s law, or more importantly, how voltage drop, resistance, and amperage all relate to each other. Learn how to implement a testing technique that will discover underlying circuit faults, even if the circuit doesn’t function at that time. Make the accurate diagnosis THE FIRST TIME and prevent comebacks, regardless of the vehicle type or circuit being addressed.
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[@cjmazdatech]

I've got several test lights of varying draw for just such occasions from quarter amp to 4 amp, all tested and labeled with their draw on them and a bunch with banana jack ends. Great video as always!

[@brandonsteckler3417]

Awesome, thank you!

[@sheerwillsurvival2064]

Keep these coming helps the old guy get back into it

[@brandonsteckler3417]

You got it!

[@ThunderbirdRocket]

Nice 👍🏼 call ! Seriously !! I hope so too !!! 🎯

[@peacepoet1947]

A fuse or relay was bad. I had a bad relay on my 94 GMC. A few months later I had to replace the fuel pump. The mechanic didn't seal the gasket on the gas tank and the vehicle failed to the smog test. I personally dropped the gas tank and put in a new fuel pump assembly unit. The engine needed an O2 sensor. No code was shown on the code reader. 😅 I was very happy to finally pass the California smog test.

[@ThunderbirdRocket]

Very satisfying feeling solving the problem and saving money !

[@ThunderbirdRocket]

Valuable topic ! Great presentation Brandon !! Crystal clear coaching , no bs , trade secrets handed out !!! Love it . Thanks mate . 👊🏼 🔥 🏹 🎯 Voltage Drop Testing for the win !!

[@brandonsteckler3417]

Thank you!

[@petar443]

You're the best Mr. Steckler. 11:35 Thanks to this explanation now i fully understand why i changed 4 electric fuel pump motors on a Toyota and each new one was failing within a month(even an OEM one). This was 7-8 years ago. I remember i received incomplete/half the answer from Mr. spelunkerd who also have a youtube channel, but now i got the complete answer from you. Thanks. And the problem was - because i was changing the electric motor only (some fuel pump units , give you the chance to change the electric motor only) , not the whole "fuel pump module/sender unit" i found my voltage drop was on the wires inside the sender unit. You know the wires that are inside the sender unit and connect to the electric motor itself and also the fuel gauge float sensor. Back then i actually knew pretty good about voltage drop and circuit load testing. So i used 9006 bulb to load test the circuit at the fuel pump connector. Not only that , but i voltage drop tested it with multimeter while the light was glowing bright. But as i said - latter i found the voltage drop was on the wires inside the module..So the 5th time i replaced the whole module/unit and problem was gone.

[@brandonsteckler3417]

Yes! My point, exactly! 🤜🏻🤛🏻

[@imfloridano5448]

Yep keeping your skills updated is always a great benefit to yourself and others you choose to help

[@MotorAgeMagazine]

My thoughts, exactly!

[@joserodriguez2632]

Escellent presentation Brandon,I just learned something new.you see your videos are among the best in you tube.please keep them comming.God bless you.

[@MotorAgeMagazine]

Thanks so much!

[@anthonysova7117]

Voltage drop for the win Yes sir VD=IxR turn the circuit ON Great presentation BRANDON Counter EMF adds resistance decreases amp draw CHEERS thanks for your demonstration

[@brandonsteckler3417]

Thank you!

[@oddlurva7641]

Thanks for this Åge. Well first I don't understand anything?? Just kidding haha . I got a little lost today too. Now understand why the Fiat 500 is not used to haul large loads of timber. Many thanks to you Åge😁

[@vicpetrishak7705]

An old round Stewart Warner ampere gauge from live current to ground reading . Short time testing before burning a fuse and also checking grounding with current and the ampere gage . Thank You , very informative !

[@ThunderbirdRocket]

Love the old school well made equipment .

[@raviautoscanning]

Great explanation. Thank you

[@brandonsteckler3417]

Thank you!

[@spirokattan3655]

Great info. Great series. Thank you Brandon!!

[@brandonsteckler3417]

Thank you, Spiro!

[@7minnow]

GREAT JOB!!!!! Brandon

[@brandonsteckler3417]

Thank you!

[@DJ-tn7vj]

Excellent video Brandon

[@brandonsteckler3417]

Thank you!

[@nickayivor8432]

Outstanding tutorial ,BRANDON STECKLER MOTOR AGE 👍 QUICK-WITTED, BRANDON STECKLER MOTOR AGE Can't wait for the next training video My mentor,BRANDON STECKLER MOTOR AGE From Nick Ayivor from London England UK 🇬🇧 ⏰️ 21:34PM Good Evening

[@nickayivor8432]

Quick Ending Please do part 2 SHREWD, BRANDON Steckler Motor Age

[@DTEAuto]

Thanks for the good lesson and reminder!

[@brandonsteckler3417]

Thanks for watching!

[@brianwalk108]

Here’s a fun one, for 20 years I checked fuses with an ohmmeter. No resistance = good fuse, right? Wrong. I had a fuse with 0 ohms but when checking it for voltage, one leg had 12.6V the other leg had 5.8V. Fuse looked fine, had continuity, but couldn’t carry any current! This fuse would have fooled an LED test light as well.

[@bernardocisneros4402]

1 in a million but it does happen.

[@brandonsteckler3417]

Spot-on!

[@luismartinez1824]

Great presentation Brandon.

[@MotorAgeMagazine]

Thank You!

[@secretsquirrel9722]

I know it's not the point of the lesson. But what was the fault? Burnt relay contact? Thanks for the knowledge Brandon!

[@brandonsteckler3417]

There was voltage drop in the fuse box (spread terminal).

[@mikechiodetti4482]

Good info, and it works.

[@brandonsteckler3417]

🤜🏻🤛🏻thanks!

[@robertmobileman8304]

Nice one Brandon , goid job

[@brandonsteckler3417]

Thank you!

[@tedlahm5740]

The loads are in SERIES. Voltage drop will equal total voltage source. In series circuit CURRENT is equal thru-out the entire circuit voltage drop DIFFERENT at each load depending on residents. Kirchhoff’s voltage law, series circuits. comment please

[@brandonsteckler3417]

You got it!

[@ThunderbirdRocket]

Thanks for sharing this information .

[@gadasavideos8564]

Exactly same problem with a riding mower starting solenoid. 12v on the activation lead but not enough current. Bad connection at keyswitch

[@ThunderbirdRocket]

Good 👍🏼 find . Thanks for letting us in on the fix you did .

[@knock904]

good lesson brian

[@MotorAgeMagazine]

Thank You!

[@romanjaspe4172]

Thanks

[@MotorAgeMagazine]

Thank you!

[@crasher88]

Brandon two questions for you at the 13 minuter mark you were discussing how unwanted resistance before the fuel pump will cause a reduced ammount of avaliable voltage to the pump. you say that reduced voltage will cause the fuel pump to be damaged, how? what is happening in the pump that would cause the damage. i was always thought to substitute the load with a comparable test light to stress the circuit. my question is how do you know what size light to install in the circuit. you can measure the resistance of the good or look it up on service data but that is not always a reliable way to come to that answer.

[@brandonsteckler3417]

Great questions… When a pump isn’t supplied properly, it spins slower. The lack of rotational speed allows the brushes/commutator to burn (over time), because the current flowing through the brushes produces heat. A normal functioning pump spins faster and creates counter-voltage, reducing the heat across the brushes. I use the fuse as a clue to indicate expected pump current load. Circuits are usually protected to approximately 2x the circuit load.

[@swav100]

What about a "loadpro" or are you against it like eric o or ivan

[@brandonsteckler3417]

My opinion only…. Devices like that take a simple concept and make it confusing for me. I prefer to load-test the circuit as I described. That said, devices like that work as designed, but they indeed have limitations (like everything else). And, if you are not sure of those limitations, you will make a mistake.

[@playharder1435]

Honda tech could have also "Ohm" tested the primary winding on the pump before replacing.

[@brandonsteckler3417]

Not necessarily…when resistance is out of range an issue is present. However, resistance is a static test and may not reveal the fault until the system is loaded. This is why the voltage-drop test saved the day

[@playharder1435]

Understood. An open in the pump's primary could quickly make the pump a suspect (before replacing) is what I meant.

[@sheerwillsurvival2064]

Wait what Hondas need fixing 😉

[@brandonsteckler3417]

🤣

[@ThunderbirdRocket]

Ha ! 😀. Yeah Hondas are pretty good 👍🏼 ! They usually run as smooth as sewing machines !! ✅ . But be at the ready . 👊🏼

[@SEDHACARREPAIR]

Morning sir Missing part 2 Video not full

[@brandonsteckler3417]

There is no “part 2”. I’m sorry but I’m not sure of what you are referencing.

[@SEDHACARREPAIR]

@@brandonsteckler3417 IMPORTANT I checked 4 times now All your other videos ended saying goodbye and finished properly This one doesn't Please check the VIDEO end at your earliest convenience. Sorry to bother you I understand the whole point anyhow Will put a sticker on my test light now to remember YOUR VIDEO. LOAD TESTING AT THE CONNECTOR NEED TO BE DONE WITH THE LOAD OF SAME RESISTANCE VALUE. FOR THAT I WOULD NEED A VARIABLE RESISTOR THAT I WILL CHECK THE RESISTANCE WITH THE MULTIMETER BEFORE THE PUT IT ON THE CONNECTOR FOR A LITTLE WHILE. AND WILL WATCH FOR THE CURRENT THROUGH FUSE BUDDY OF LIMIT.

[@brandonsteckler3417]

Thank you, I will get this sorted

[@MotorAgeMagazine]

Apologies for the glitch. We have made a correction in the description to reflect the missing portion of the video

[@derekmoult238]

As an aircraft electrician I always do at least 2 tests. Check for voltage AND test pump resistance. Takes seconds and confirms everything...