Help diagnosing P0641 fault

[SeanB833]

Need help finding out what’s causing the P0641 fault. This is accompanied by a flashing glow plug light and every now and then EML. This fault is intermittent. I’m able to clear it and drive the car for a few days before it returns.

The only development I’ve had is that my O/S xenon has stopped working. The bulb is fine, and I had suspected the ballast module. I removed the head light today and found the main plug into the head light was heavily corroded and one of the terminals has snapped off. Also, upon removing the ballast module, server corrosion was found there too.

Can this be causing the P0641 fault?

 

[mty12345]

17026/P0642/001602 - Ross-Tech Wiki

wiki.ross-tech.com

This is the closest code i could find on it. I believe your code is just 'Open circuit' rather than 'low' , but it still relates to the 5v reference signal.

5v reference is a 5v voltage generated by the ECU, and used by a lot of engine sensors to work. If that isn't there then the ECU is having to guess at the readings of those sensors. It will either be a wiring problem, possible corrosion inside the ECU plug containing that 5v pin, or possibly an internal fault with the ECU itself. Hope that helps

 

[SeanB833]

17026/P0642/001602 - Ross-Tech Wiki

wiki.ross-tech.com

This is the closest code i could find on it. I believe your code is just 'Open circuit' rather than 'low' , but it still relates to the 5v reference signal.

5v reference is a 5v voltage generated by the ECU, and used by a lot of engine sensors to work. If that isn't there then the ECU is having to guess at the readings of those sensors. It will either be a wiring problem, possible corrosion inside the ECU plug containing that 5v pin, or possibly an internal fault with the ECU itself. Hope that helps

Appreciate that bud! I don't suppose you could point me to a wiring diagram?

 

[mty12345]

Appreciate that bud! I don't suppose you could point me to a wiring diagram?

No worries. I don't know of any free wiring diagrams. The official ones are here, so you'd have to pay for an hours access and then download what you need. https://erwin.seat.com/erwin/showHome.do

I think it's less than £10

 

[SeanB833]

Update:

I've gone through the current flow diagrams and located the 5v wire. The sensors that are connected, Engine speed sender, Throttle valve potentiometer/throttle valve module, postion sender for the charge pressure positioner, EGR potentiometer/ EGR valve.
I've con-checked from the ECU plug to each sensor via that wire and all are good.
I've voltage checked them also and they are all good.

I'm guessing it's probably a sensor or one of the valves are not working correctly. About to pull off the throttle body and pray that's the issue as the egr is buried down the back of the engine. The turbo won't be ideal either.

When the codes are cleared the car runs absolutely fine. No power issues or smoke. I did have my DPF light come on about a year ago but after re-gening nothings come back since. The flashing glow plug light with intermittent engine light started not long after though. Which leads me to the EGR.

Any other checks or ideas would be much obliged?

I've also attached the wiring diagram.

TIA.

 

[SeanB833]

Another update:

I've just noticed a blanking plate on the block side of the EGR pipe that runs from tbe throttle body to the block.

I have no history regarding the EGR being blanked. I had the car for 2 years before any issues. Any chance, (if this wasn't mapped out) this could be an issue? Feels like it would of flagged up sooner if it was an issue.

 

[mty12345]

It sounds like you're doing a good job in checking everything that needs to be checked mate. These kind of intermittent faults are the worst to troubleshoot. Not sure what else to suggest really. In my experience it's usually the wiring and components that get hot that are most likely to be at fault, but when you have so many sensors on one reference it's difficult.

If you know someone that has VCDS then could be worth plugging it into that and seeing if there are any more detailed codes which may help. The P codes are generic OBD2 codes, whereas VW have 5 digit codes that can be more specific.

Edit re EGR: Like you say though i wouldn't have thought the actual deletion would be the issue, but if the EGR has been deleted and it's wiring plug is not connected to anything, that would be a prime suspect for some sort of corrosion/water ingress issue etc. If the plug still has a 'live' 5 volt reference in the connector, there is a chance that it's finding a high resistance path to ground. Not enough to blow the fuse, but enough to pull the voltage low etc. Worth a look for sure.

 

[SeanB833]

It sounds like you're doing a good job in checking everything that needs to be checked mate. These kind of intermittent faults are the worst to troubleshoot. Not sure what else to suggest really. In my experience it's usually the wiring and components that get hot that are most likely to be at fault, but when you have so many sensors on one reference it's difficult.

If you know someone that has VCDS then could be worth plugging it into that and seeing if there are any more detailed codes which may help. The P codes are generic OBD2 codes, whereas VW have 5 digit codes that can be more specific.

Edit re EGR: Like you say though i wouldn't have thought the actual deletion would be the issue, but if the EGR has been deleted and it's wiring plug is not connected to anything, that would be a prime suspect for some sort of corrosion/water ingress issue etc. If the plug still has a 'live' 5 volt reference in the connector, there is a chance that it's finding a high resistance path to ground. Not enough to blow the fuse, but enough to pull the voltage low etc. Worth a look for sure.

Hopefully will get it plugged in to VCDS this weekend.

The EGR sensor was plugged in. Everything looked fine with the plug side. Couldn't see the sensor side.

Appreciate the reply. I'll see what VCDS has to say.

 

[SeanB833]

Went back over my wiring checks today and found this: Multimeter fluctuations.

I've con checked the wire and thats fine. Any ideas?

 

[mty12345]

Went back over my wiring checks today and found this: Multimeter fluctuations.

I've con checked the wire and thats fine. Any ideas?

Video set to private

 

[SeanB833]

Video set to private

My bad, try again

 

[mty12345]

What wire/circuit is that from?

 

[SeanB833]

Another update. I've put everything back together. Cleaned up the throttle body. Cleared the codes. Noticed theres a throttle postion gauge on the obd app. Its reading 1.57% with the engine running and off. Moving it with my fingers doesn't change the value either. Guessing this is shot? Or could it still be the wiring/ ecu?

I'm now getting these codes instead of the P0641(psb). I'm unable to clear them as well. All these are on the 5v ref circuit.

The fluctuating reading on the multimeter is still there as well.

 

[SeanB833]

What wire/circuit is that from?

It would normally see battery voltage. In the diagrams above its the purple wire and purple brown wire going from ecu to throttle valve potentiometer and the purple green wire going from ecu to the egr sensor.

 

[mty12345]

Hmmm, that's a difficult one mate. Given the various fault codes, (some high, some low) plus that fluctuating voltage on what should be 12v, makes me wonder if you have some sort of short between the 5v reference and the 12v from the battery? Maybe disconnect all the power and measure the resistance between the 5v ref and that wire that should be 12v, and see if you have a short between the 2 somewhere.

As for the throttle sensor readings, are you sure if it's the pedal potentiometer position, or the one on the throttle body? Sometimes the labels aren't correct on live data. Even if you are sure it's the right one, then without the 5 volt reference being correct/present then you could get all sorts of weird readings or none at all.

Only other thing i would suggest is maybe unpluging each sensor that uses the 5v ref one at a time, then seeing if you can delete the codes etc. If the fault is with a sensor rather than the wiring, then hopefully the rest of it will come back online when the bad sensor is unplugged. Obvs you'll get other fault codes relating to the sensor that is unplugged, but if the 5v reference codes disappear that is the key.

 

[SeanB833]

Hmmm, that's a difficult one mate. Given the various fault codes, (some high, some low) plus that fluctuating voltage on what should be 12v, makes me wonder if you have some sort of short between the 5v reference and the 12v from the battery? Maybe disconnect all the power and measure the resistance between the 5v ref and that wire that should be 12v, and see if you have a short between the 2 somewhere.

As for the throttle sensor readings, are you sure if it's the pedal potentiometer position, or the one on the throttle body? Sometimes the labels aren't correct on live data. Even if you are sure it's the right one, then without the 5 volt reference being correct/present then you could get all sorts of weird readings or none at all.

Only other thing i would suggest is maybe unpluging each sensor that uses the 5v ref one at a time, then seeing if you can delete the codes etc. If the fault is with a sensor rather than the wiring, then hopefully the rest of it will come back online when the bad sensor is unplugged. Obvs you'll get other fault codes relating to the sensor that is unplugged, but if the 5v reference codes disappear that is the key.

I'll check those suggestions now. Just noticed my fuel position sensor is also on that circuit.

I've plugged it into vcds. Code remain. I've attached the fault log. Car now is in full on limp mode.

 

[mty12345]

I'll check those suggestions now. Just noticed my fuel position sensor is also on that circuit.

I've plugged it into vcds. Code remain. I've attached the fault log. Car now is in full on limp mode.

Have you done a throttle body readaption/relearn after cleaning it? If that not then that might account for the limp mode, either that or the lack of fuel pressure data is causing it.

 

[SeanB833]

I have not. I have tried functioning the throttle though vcds and it wont let me. A message comes up saying 'refused by control module'

I've gone back through all my checks. Con-checking everything wire from sensor plug to ecu on all 5 sensors on the 5v ref circuit. They are all fine, 0.5ohms.
I've con-checked the grounds from plug to ecu and ecu to chassis. They are all fine as well.
I've checked the voltage at each plug. Egr, Throttle, Fuel and speed sender all receive 5v. The Turbo does not. None of the 5 sensors receive 5v at the 5v ref wire.
I'm still getting the fluctuations on the EGR and throttle sensors at what normally read Bat voltage. These are also the only sensors that are more than 3 wires.

On vcds I opened up each sensor to view what voltage they are displaying. With ignition on, the fuels showing 4800.2mV, Throttle 92.6mV, EGR and turbo 0.0mV.
When unplug the throttle sensor that jumps to 4999.8mV.

That's all the evidence I've collected. The original fault codes gone now and its been replaced with all these other codes. With the addition of the fuel one.

 

[SeanB833]

Update:

No continuity issues between different wires.

Managed to clear all the faults except the fuel pressure sensor that wont budge. When I start the car all the other faults come back.

Belows the codes that now appear. All still the same sensors on the 5v ref, but the speed sensors coming up now.

 

[SeanB833]

Summary:

Initial fault P0641 Sensor Reference Voltage “A” Circuit/Open.

Wiring diagrams:

Checks carried out and results:

Put everything back together, plugged in VCDS. The original fault has been replaced by all 5 sensors on A circuit. Test results are attached.

Decided to test the motor on the ASV. As shown on the spread sheet, here and the egr motor give me weird voltage fluctuations. See thjs video: https://youtube.com/shorts/D-cEnCqN6Mo?si=UjP9GSjzSsDpDKjB I’m unable to output test anything due to ‘refused by control module’ message on VCDS. Actuating by hand cases do not change readings on the multi-meter, across the variable resistor. The flap is also fully open and fails to move under any circumstance.

Im struggling to makes much of all this. I feel like im chasing my tail at this point.

If anyone has anymore suggestions, please fire them my way!