P0118 Coolant Temp-New sensor didn't fix it DIY Diagnosis Pt1

[@jadonpossinger7953]

I'm going to try and explain this, as it was explained to me and greatly helped in my diagnosis of 5V sensors. 2 wire sensors are pull down circuits they have a 5v and ground wire. The PCM sends 5V and measures it when resistance increases the voltage drop approaches 5v so unplugged sensors read 5v as there is infinite resistance between the wires. 3 wire sensors are pull up sensors. they have 5v, a direct ground and sense wire. As the position on the potentiometer changes the signal voltage moves according to the retuning voltage of what's left and when unplugged will read 0V as there is no connection from voltage to the measured wire. mostly this information is useful when you are tying to work out where the issue is lying on a fault the wire the ECM or the sensor. IE a pull down circuit that shows 0V is almost always short circuited in the wiring harness before the sensor. or a pull up sensor that reads 5v is very likely shorted the V5 to the sense wire from rubbing or something similar.

[@nowayjose596]

ECT sensor is an NTC (negative temperature coefficient) thermistor so as temperature increases then resistance actually decreases. If the sensor/wiring was working properly you'd see the voltage drop across the sensor (which is what the PCM is looking at) start out higher when the coolant temp is cold, then continue to decrease as the car warms up.

[@nowayjose596]

Fixing the ECT sensor issue should probably help/solve the difficulty with (re)starting after it's hot. Since the PCM (erroneously) thinks the engine is super cold, it's adding a bunch of fuel that would normally be required to get enough to vaporize for proper start-up in those conditions. However, since it's not actually that cold, it just creates an overly rich condition. That's why you can get it to catch and start by opening the throttle to let more air in to briefly offset that and create a mixture more conducive to combustion. It probably helps that this vehicle has a cable operated throttle body so you have direct control over how much air is entering the engine - an electronically controlled throttle might not let you do that, but I couldn't say for sure. And I know our hero here knows all this, just putting this out there for others reading the comments who might not know how/why the difficulty getting it to restart after it's warm is related to the ECT code/fault.

[@SchrodingersBox]

Exactly correct!!!

[@Mr2004MCSS]

Usually a two wire coolant temp sensor for the ECM indicates that there will be another sensor for just the gauge. The CTS on my 92 Cavalier is a three-wire sensor and one wire is for the gauge. From what you could tell, did the CTS sensor that you could see look like it had been changed?

[@nhitc6832]

Would love to be a mechanic DIY but my beater Civic absolutely refuses to break down 😆. Meanwhile, I'll just enjoy watching someone do diagnosing.

[@SchrodingersBox]

Hahahahaha. I have had a number of people who have told me similar. They are so excited about some of the things they learned they wish their car would break down so they can figure it out lol!!!

[@qre268Zrtb]

Hi Matt, it is absolutely fascinating watching you diagnosing issues, using sound logic. when I look at issues with my car, I think hmmm how would Matt start the process of finding the problem.

[@SchrodingersBox]

Great to hear! I don't see any other way to do it!!

[@mkoteb7202]

Mate, you made a mistake. Temperature sensor don't have a 5V reference. The sensing circuit is 5v through precision resistor which act as a voltage divider with the negative temperature coefficient resistor (the temp sensor) which must terminate to a ground to complete the circuit. That ground sometimes is shared internally in ECM (that isn't the case here)

[@aarongallagher8898]

I would before taking plenum off measure the ground side of temperature sensor. Or give it a good ground. From another access point. Or maybe unplug pcm and do continuity through temperature sensor circuit to verify a open.

[@SchrodingersBox]

We saw continuity to ground on the sensor return though. No need to provide a ground. We know there is reference and ground - the issue can only be either at the sensor or under the intake manifold. Either way that’s how we know we have to go there.

[@Lou-eye]

My wifes 2003 ford ranger has 2 coolant temp sensors under the plenum and my sons 2011 ranger has just one. Changed them out (without pulling the plenum)on both rangers and it fixed their hard cold morning starts.

[@simonilett998]

Not forgetting, thermistors and potentiometers never share the 5V reference with other sensors, the shared wires had to be the ground/low reference wire👍 We're down to 4 possibilities: Faulty 'new' sensor. Broken ground/low reference wire between the sensor and common harness splice. Broken signal wire between the sensor and PCM. Loose pin fitment at the sensor connector🤔 Intake has to come off unless you can manage to unplug the connector from the sensor to do further tests there.

[@jum5238]

I like your shirt. Goes along with a bumper sticker I have that says, "Does your TV teach you to believe that?"

[@fredflintstone4715]

After replacing the radiator on my 98 Ranger, the temp gauge hasn't been right. Seems to always read way low compared to before, but the live data seems to be just fine. Seen the temp sensor under everything in the way, so decided not to replace it. Then was told there was two sensors also, but never did look for the other since the live data always seemed correct...

[@woody95124]

Very detailed work...your good....

[@khaliltazi7692]

Correct me if im wrong but thermistors cannot share 5v ref but they can share grounds with other sensors

[@SchrodingersBox]

That’s correct

[@tomtke7351]

I made a simplistic comment earlier that three wire sensors are voltage sense whereas 2 wire are current. I want to add clarity as the ECM reports the results of a two wire as a voltage. Where does this reported voltage come from? Brief overview: (-1-) THREE WIRE: ☆one wire: to fixed voltage (+5V) ☆one wire: to ground (gnd) ☆one wire: sensor signal to ecm as some voltage that's in between +5V and gnd. This is a variable voltage that the sensor coorelates with its position. Its a potentiometer. (-2-) TWO WIRE: ☆one wire to gnd ☆one wire to ECM. The sensor varies its resistance in relation to sensor's operation (i.e. temperature as example.) The ecm's job is to measure this sensor's resistance (by measuring its current flow.) Ohm's law says R = V/I. The ecm applies a fixed voltage source (internal ECM reference) thru an ecm resistor then thru the sensor's resistance. When sensor's resistance drops the current flowing thru sensor increases and voltage drop across ecm's resistor increases too. By measuring voltage across its internal resistor the ECM is measuring sensor CURRENT. If a fixed voltage is applied across a variable resistor (sensor) the only change would be current. (A fixed voltage never changes.) QUESTION: If a 2-wire sensor changes value (resiatance) and so current flowing thru it does too... how will the voltage change... example if I = 2ma and R = 1000 Ohms V = 2V if I = 1ma and R = 2000 Ohms V = 2V VOLTAGE DID NOT CHANGE ALTHOUGH R DOUBLED The only way to 'detect' this change in current thru the ECM's fixed resistor. UPDATE -- The temp sensor varies its resistance vs. its temperature environment. The result is a change in voltage dropped across the ECM's INTERNAL RESISTOR. If measuring the sensor's voltage it's really measuring voltage across the ECM's internal resistor.

[@marshall1157]

Great T-shirt!

[@asonofgod_98]

Hey Matt, it’s been a while, feels like it’s been half a year lol 😂. Will watch this after Church. Brighton from Zimbabwe 🇿🇼👋🏾

[@SchrodingersBox]

Welcome back!! Good to see you again.

[@mauroarantes9407]

I LOVE YOURS VIDEOS...

[@nickayivor8432]

Can't wait for the next video Enjoy your evening Schrodingers Box 👍 SHREWD Schrodingers box From Nick Ayivor from London England UK 🇬🇧 ⏰️ 11:22am Good Morning 🙏 🌄

[@SchrodingersBox]

Always appreciated my friend across the pond!!

[@DylanL69]

That 4.68 v I believe is the circuit voltage because it's an open circuit may not be the reference

[@SchrodingersBox]

It’s the reference. It’s full reference voltage. Disconnecting the sensor would give exactly the same reading

[@DylanL69]

@@SchrodingersBox yeah the problem is the signal return wire most likely corroded or some accident damage still could also be the pcm not grounding it out

[@toddb930]

Maybe the engine starts fine when it's cold but when it heats up a little it has a hard time?

[@SchrodingersBox]

Yes thats definitely the case- when the engine is cold is needs extra fuel to start but when its warmed up, the perceived cold engine temp is flooding it.

[@dereksimenac8844]

Why would you suspect a 5v reference issue when you had 4.6 volts on the coolant temperature sensor?

[@SchrodingersBox]

There isn’t. The one thing we know is this is NOT a 5V reference issue. This is an open circuit issue- 5V reference is being sent out.

[@ChristmasCrustacean1]

only time I'd say "might as well do it anyway" applies is for a timing belt if you're changing a water pump.

[@Ironblank1]

Do you know what can cause a check engine light self test to be off but comes on when engine starts? It’s a friend who bought a Hummer 2 or 3 . The car is not passing emissions has a bad converter but I figured that he better fix the light not coming on self test first.

[@SchrodingersBox]

Never heard of that. So you are saying the light does NOT come on with key on engine off but it comes on after starting the car and stays on? What codes are you reading from it?

[@Ironblank1]

@@SchrodingersBox Exactly! Check engine light off ( key on) Sorry I should have included this info. P0420 , B2961 Key In Ignition Circuit Malfunction Heating And Air Conditioning (HAC): 1 DTC(s) B0229 Recirculation Position Feedback Circuit Range/Performance

[@SchrodingersBox]

Wow that is a new one to me. I would say the check engine light failing to come on during KOEO (Key On Engine Off) is most likely related to the B2961 as the key is not being detected in the ignition. When the key is inserted it closes a switch that lets the BCM know to turn off the alarm and anti-theft. This switch has failed and It seems that it must have been bypassed somehow because attempting to start the car with that code present should sound the alarm and of course also initiate the anti theft’s shutdown of fuel and spark but clearly it doesn’t. I wonder if all the other dashboard lights come on too or if others fail to come on during KOEO which would indicate those are also linked to the BCM.

[@Ironblank1]

This is what I’m afraid of. The guy bought it at a used car dealership. If someone bypassed it intentionally, he’s going to be in trouble cause I’ve had a hard time finding a good mechanic and I don’t know if I want to take on this. He has a week before his temporary license expires. I’ll keep you updated. Thanks for replying as always.

[@SchrodingersBox]

Yes I agree- if the emissions place properly does their inspection they will check for the KOEO engine light. And of course you can’t prove the light works by having the legitimate codes (P0420) light it up because then the car would fail for having the light on while running. I think the ignition key missing code may in itself light the check engine light while running so there’s no way around it- it has to be fixed. That sucks.

[@jimharper6073]

First again... for real this time...

[@SchrodingersBox]

By gum you are indeed!

[@williamwhite9767]

Excellent!

[@johnaclark1]

So, you have 5v from the PCM to the sensor (presumably) and the PCM is proven good and able to read the circuit, but how do you know there is not a break in the signal return between the sensor and the splice for the signal return for all the other sensors? Is that section of wire all under the intake? I also have a question as to why the temp gauge works but the ECT is reading 4.6 and you're getting 5v on the signal at the PCM.

[@SchrodingersBox]

Yes it is indeed possible the open is on the signal return prior to the first junction. However- that junction is also under the intake. So either way the intake must be removed.

[@jadonpossinger7953]

I suspect the issue is the last person was lazy and did not remove the intake damaging the plug on the wiring harness

[@johnaclark1]

@@jadonpossinger7953 That, or a junk aftermarket sensor, or a broken wire on the signal return. Those are really the only 3 possibilities.

[@SchrodingersBox]

How did they remove the sensor without removing the intake??

[@SchrodingersBox]

The other possibility is an open on the feed towards the sensor

[@jgeorges3061]

Matt, You rock brother as always AWESOME explanation and thought process waiting for part two. cheeeeeeeers

[@SchrodingersBox]

Thanks as always my friend. Part 2 won’t disappoint!

[@midik123]

Shared signal return? How then does the ecm know, wich signal comes from which sensor?

[@tomtke7351]

would the signal at ecm be a voltage thru an intetnal divider such thst variable temp sensor resistance causes varying current thru sensor varying ecm voltage divider results?

[@SchrodingersBox]

Good question. It measures from the output at the PCM- not at the signal return. The signal return is strictly a ground. The voltage drop is measured from the voltage source at the PCM across an internal resistor. In this specific case there is no voltage drop across the internal resistor because there is an open circuit.

[@tomtke7351]

Might make a basic observation: that a three wire sensor monitors sensor voltage while a two wire measures current.

[@SchrodingersBox]

No, the two wire sensor thermistor definitely measures voltage.

[@SchrodingersBox]

No-the 2 wire thermistor definitely measures voltage. Voltage drop, specifically.

[@JimFinlayson]

Thanks for the continuing education.

[@SchrodingersBox]

Any time!

[@samsonmogire4959]

your website has no option to unsubscribe

[@SchrodingersBox]

there is- under your account tab is an unsubscribe button which gives instructions on discontinuing your PayPal or stripe service which cancels the subscription. email me if you need help

[@l.c.9596]

Do you have a link for this scanner? Thank you

[@smc9764]

You can Google them. A good alternative, which is nearly identical is from ThinkTools. I bought one for about 1k and they also have the same scope. Ivan at Pine Hollow uses the ThinkTools version.

[@SchrodingersBox]

Not only a link but a full review and tutorial. Search my channel for “Topdon”.

[@sheerwillsurvival2064]

I would say get a shirt comment while you still can, but that’s too late they already censor our comments

[@samsonmogire4959]

am your subscriber on youtube and also on the web site am unable to unsubscribe please do it for me am unable to put money on my bank account because of that i cant load money on my account

[@SchrodingersBox]

You have to go to the PayPal site and cancel under your account. I can do it for you but I need your email address. Send me an email to [e-mail] and I will a be happy to do it.