2010 Jetta P0641

Anyone have any experience with this? There were a couple threads here when I searched, but with seemingly no resolution.

The car in question is a 2010 sedan, CJAA+manual, DPF/cat delete a long time ago, closing in on 1/4 million miles, perfect service history.

Came in cranks/no-start. Has this hard DTC P0641 sensor reference voltage A circuit open. It also had a DTC for the accelerator position sensor (I forget the exact one), but that clears and did not come back. I did unplug the pedal and see if I could clear the P0641 and it just comes right back (thinking maybe the 5v reference output was shorted inside the pedal sensor).

The three main powers and grounds to the ECU are good. I have 5v at pin #1 on the G185 pedal sensor, but nothing on pin #2 for the G79 pedal sensor, although the data works normally in VCDS when you move the pedal. Glow plug light flashing. Cranking RPM, rail pressure, are normal.

Going to dig further into this just swamped with work this week figured if anyone had any clues.

Quick update: Measuring Group 030: G79 voltage (Block 1) stays 0, G185 (block 2) goes up to ~5v like normal during pedal sweeping. I am thinking the 5v reference from the ECU to this particular circuit is dead. What I don't understand is why it won't run, or at the very least start and idle, without that [redundant] circuit working, unless there is another 5v that is also dead. All the sensor 5v references go directly to the ECU individually, there is no splicing anywhere that I can see in the diagram, which leads to something "bad" inside the ECU itself.

So in case anyone stumbles across this, wanted to update what I found once I finally had time to mess with it.

Decided to go and one by one check for 5v reference at all the sensors that use it. Some items this is spliced inside the harness, some items get 5v on a dedicated wire straight from the ECU. However, even these are internally bused inside the ECU. So this is what is tricky.

For instance, the J883 exhaust flap module has its own internal position sensor, that sensor's 5v reference as well as both the G450 and G505 exhaust/EGR pressure differential sensors' 5v reference are all shared on one pin #14 on the ECU, and the wiring diagram actually labels is '5V MK1'. This would be a "non-essential" suite of sensors, as if either or all of these were not working, the engine would still start and run.

Other 5v references are not labeled 'MKx", but usually show at least a '5v' and the ECU pin.

So I got to the intake runner control module's position sensor, G336, and found no 5v reference there, either, just like the one leg of the pedal sensor I mentioned above. The G336 shares its 5v with the CMP sensor G40, from pin #10. So, I went to unplug the G40 (which on the CJAA is sort of buried down below the intake... in the same orientation and bracket arrangement as on other TDIs, like the BRM for instance, but the PD's giant intake covers it). Upon doing so, I bumped the harness where it rubs against the oil filter cap, and immediately heard the intake runner motor start working (the key was on). When I went to see if I triggered any further DTCs, I found the tach jumping around.

Then, I found I could push in a very specific spot on the harness and make some strange stuff happen.

So, in the same manner as the BRMs, this CJAA has a bad engine harness. UNlike the BRM, it is twice as much money, and looks to be more involved to replace.

We'll see, I will update again.

New engine harness fixed it. Big job, labor intensive. Much more so than the BRM harnesses I have done so many of.



But being patient and taking my time got it accomplished with no issues.

Had to remove the thermostat assembly, so at 260k miles it got a new one. Had to remove the dipstick, had to remove the vacuum pump, so it got a new gasket. Other than that, no big deal.

Well that's a big job in the end!!! Do you know "where" exactly in the harness the problem is, or will you rip it apart to find that? Yes, I understand for you that time is money, but just curious how far you may go to learn about it!

dhuddleson said:

Well that's a big job in the end!!! Do you know "where" exactly in the harness the problem is, or will you rip it apart to find that? Yes, I understand for you that time is money, but just curious how far you may go to learn about it!

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oilhammer said:

.......Upon doing so, I bumped the harness where it rubs against the oil filter cap, and immediately heard the intake runner motor start working (the key was on). When I went to see if I triggered any further DTCs, I found the tach jumping around.
Then, I found I could push in a very specific spot on the harness and make some strange stuff happen........

Click to expand...

oilhammer said:

New engine harness fixed it. Big job, labor intensive. Much more so than the BRM harnesses I have done so many of.

But being patient and taking my time got it accomplished with no issues.
Had to remove the thermostat assembly, so at 260k miles it got a new one. Had to remove the dipstick, had to remove the vacuum pump, so it got a new gasket. Other than that, no big deal.

Click to expand...

Your just a party animal, aren't you?
I think I would have cut the harness open in that area to see what was going on.
Than again I am a bit frugal.

Do not have the time. And the cost of labor becomes the cost of trying to repair a 10 year old 260k mile harness that I cannot warranty a foolish move. I have also experienced with BRM cars that harness issues quickly turn into a whack-a-mole game with the car constantly returning with recurring problems. I cannot have that for my customers. If someone wants to pay the shipping I will gladly box up the old harness and send it to you if you'd like to do an in depth autopsy.

I have twice now seen a CJAA harness rub a hole through the oil cooler... and this one had a shiny spot working through already. So I did spend some more time securing it better than the factory did, as well as place a little foam spacer on the cooler. The little leg of the harness that goes to the coolant sensor in the lower radiator hose is what does it. Wish I got a picture of that. I also wrapped some extra cloth covered harness tape over a few spots that were clearly chaffed, as well as routed it down and away from the oil filter cap where it rubs on the edge. Now this engine's filter cap can be R&R'd without touching the harness at all. There was a teeny tiny hole in the outer covering right there, although the wires inside did not appear damaged yet. I did open a couple inches of the harness in that area. If I were to try and "fix" this, I would have still had to take everything apart as the portion that is suspect is the one that goes up the front of the block, behind the dipstick tube and outer coolant hose. If a harness had a bad spot up by let's say the vane sensor or one of the exhaust pressure sensors, and could be easily repaired (or at least a repair attempt made) withOUT taking a bunch of stuff apart, I certainly would try that first. But in this case, the buried nature of the problem area would have prevented that.

I think I better check if mine is rubbing in that area.
Glad you did post this btw.

What sucks is, there is just no easy way to get in there and do and kind of prevention. It is just in a really bad spot.

I just pulled codes yesterday from my 2011 TDI Wagon (doing an oil, filter, fuel filter, air filter maintenance cycle at ~181k miles) and it popped up a P0641 - open circuit - intermittent for me. When I double checked the mileage listed it pretty much matched up with a road trip limp mode and flashing DPF light I had back in late March as I idled along at 1472 RPM and 60 MPH downhill into Revelstoke. I pulled over in Revelstoke and shut the car down (no code reader with me that day) and when I started it back up after a quick washroom break it ran fine for the rest of the trip.

So, unrelated (or so I thought) - back in late 2020 I was getting a P2015 (and a P2016?, memory is starting to go), ordered up the DieselGeek repair bracket/block, installed it, but the code kept coming and going intermittently in 2021. I didn't actually see any drivability issues with this code coming and going so I just ignored it thinking that one day I would replace the intake to fix it permanently. The code finally stopped setting the CEL, but I don't remember when.

My kid also experienced the flashing DPF light a handful of times over the last 6 months too, but nothing that set permanently and I never did get around to pulling out my laptop and VAGCOM to check for stored faults.

After reading Oilhammer's diagnosis above (one of the first hits for P0641) I'm wondering if all this wasn't caused by a harness issue to the intake runner flap motor. Thoughts? Its all been intermittent so far and my previous P2015 and P2016 code readings were done just using a bluetooth reader and Torque, I never did pull out the laptop back then because the diagnosis seemed so simple.

Thanks, John

(P.S. funny enough I was looking at the harness right behind the oil filter cap just yesterday and thinking to myself it was odd that it just sat against the filter housing.)

(P.P.S. was I actually experiencing limp mode or could it have been something else? what would have tripped limp mode in this case?)

Since I made this thread, I've replaced four more CJAA harnesses. Various things, but it fixed every one of them. Always on an A5, never an NCS or A6 Golf.

I've not had a 100% success rate with the DG intake fix. I have had a 100% success rate installing a new intake with the updated actuator assembly.

Thanks - I'll keep tabs on it to see if it reoccurs again so I can hook up my VCDS again. I was holding off on the new intake install anyways, the CEL hasn't come back in a while, maybe during the summertime heat.

Great, one more thing to add to the list of potential problems lol.

Thanks for posting this Oilhammer. I have always looked at the wiring harness around my oil filter housing and thought "that looks way to close and hot for those wires....". Will monitor. Luckily I'm an A6 Golf.

oilhammer said:

New engine harness fixed it. Big job, labor intensive. Much more so than the BRM harnesses I have done so many of.



But being patient and taking my time got it accomplished with no issues.

Had to remove the thermostat assembly, so at 260k miles it got a new one. Had to remove the dipstick, had to remove the vacuum pump, so it got a new gasket. Other than that, no big deal.

Click to expand...

Just curious if you could post the steps on what needs to be removed in order to replace the engine harness on these cjaa engines. i have the same code and problem and im looking to replace the engine harness. looks like a pretty big job so any insight would be so much appreciated

As you can see in the pic, I removed the front of the car (the lock carrier assembly). You could probably do the job with just moving it out some, but the way the A/C lines are arranged, they don't allow for a lot of movement forward, but maybe with the little movement you could get with them still attached, along with removing the cooling fan assembly, you could get comfortable clearance on the front to easily get everything loose to gain access to the harness. But I don't like fighting things, I have an A/C machine next to me, so I just took the whole thing off. It's easy.

Then you have full access to the entire front of the engine, so getting to the harness as it wraps around the oil filter and goes back down was not too bad. There is one leg that goes over and back down the back side of the engine to the low pressure EGR valve, so that required some work.

It isn't a "bad" job, just tedious. Air cleaner, battery, battery tray, wiper arms, cowl cover, etc. all come off.

oilhammer said:

As you can see in the pic, I removed the front of the car (the lock carrier assembly). You could probably do the job with just moving it out some, but the way the A/C lines are arranged, they don't allow for a lot of movement forward, but maybe with the little movement you could get with them still attached, along with removing the cooling fan assembly, you could get comfortable clearance on the front to easily get everything loose to gain access to the harness. But I don't like fighting things, I have an A/C machine next to me, so I just took the whole thing off. It's easy.

Then you have full access to the entire front of the engine, so getting to the harness as it wraps around the oil filter and goes back down was not too bad. There is one leg that goes over and back down the back side of the engine to the low pressure EGR valve, so that required some work.

It isn't a "bad" job, just tedious. Air cleaner, battery, battery tray, wiper arms, cowl cover, etc. all come off.

Click to expand...

Awesome. Thanks for the input. I think im going to try to keep the rad cradle and everything together if i can. And just loosen the crash bar bolts enough to give me some room as i dont have an ac machine and my ac works great. Just another question. Do you think i can get away with not draining the coolant or is that just undoable in your experience. I appreciate the quick reply. I just ordered a brand new harness from FCP Euro as i live in canada and getting the harness elsewhere just isn't going to happen.

You can certainly try, that stuff is again all in the way.

oilhammer said:

You can certainly try, that stuff is again all in the way.

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Just want to update on the situation. A new wiring harness completely fixed my issue as well. I ended up not having to drain the coolant or evacuating the a/c. I removed all the bolts from the crash bar and pulled everything back about 4-5 inches without bending or damaging anything. I did have to take the dipstick off and intercooler pipe in front of the engine. Very time consuming but in the end im glad i did it because my car is fixed. Thanks again for the advice and expert knowledge

glad to hear that. will keep a eye on 2 CJAA vehicles we have. thanks oilhammer!

I’m fighting a p0651 reference voltage b circuit open. I see where the harness was rubbing on the oil filter cap but no sign it rubbed through the wiring harness tape.

I’ve checked the 5v at the egr/dpf differential pressure sensor, egr valve, cam position, intake runner motor and that one sensor on the fuel rail (tb side). I was jiggling the harness everywhere near the oil filter housing to see if I get a drop in the 5V, I don’t. The next thing I could try is seeing what kind of resistance is on the 5v wires between the ecu and the plugs in question.

I could be missing some sensors (probably am) because I can’t find a list of them lol

A few weeks ago the car wouldn’t start, it was showing egr codes. The tuner deleted the codes from the ecu. The other day it started but ran with a bad miss, misfire codes on all 4 cylinders. It runs fine when you clear the codes.

the reference voltage code doesn’t disappear with any of the sensors unplugged. All fuses both inside and outside are good. The only thing I didn’t check was ecu power and ground (I know that’s the first thing I should’ve checked) I even tried a spare cjaa ecu but I still have the same problem

I’m slightly hesitant on getting a new harness because it’s a decent bit of money and also several hours of my time, to maybe fix this. I also don’t quite have the proper resources for this project, I’ve spent the past few days looking through every tdi group for wiring diagrams and other bits of information to help me. This thread being the best.

I’ll keep digging and report if I find anything but if not I may just get a harness Monday and put it on next weekend.

Does the CJAA harness work with the CBEA in the A3? If not what are the differences?

McGuirk said:

Does the CJAA harness work with the CBEA in the A3? If not what are the differences?

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I can’t answer that for you, I only have experience with the cjaa and alh engines.
I know there is somethings different internally, cbea has a balance shaft module, cjaa does not. I could be wrong but I’ve definitely read the cjaa is more desirable for that reason. It’s popular to remove the balance shaft on the pds.

I’d do some digging, see if there is any difference sensors.

unrelated to your comment but related to the thread, in case anyone’s wondering, I did buy a harness and will swap it next weekend (hopefully it shows up) I’ll ohm out all the 5v wires to locate the break, maybe helping someone in the future. Although I’d recommend replacing the harness sometimes the funds just aren’t there and if it’s your vehicle, it’s your choice. I run out of time (and patience) and ohminh out each wire is time consuming, especially in the car. Making it harder like oilhammer said, there is a few 5v wires all internally connected in the ecu.

Funny this thread popped up, as I'm having a problem child in the shop once again and having a tough time figuring it out.

Unlike the A5 car in the original subject of this thread, this is a 2013 NCS car.

I'll post again later with more details of what I am dealing with.... McGuirk, the CBEA was never used in the NCS, so the engine harnesses will be different... and the CJAA harness is different in the NCS from a CJAA in an A5 or A6 as well. Because it's a different car.

Throwing the same P0641 fault or something different this time?

P0651, voltage reference B . So not the same as the 2010 A5 in my original post, but the same as Hayden's car in his post that revived this thread, and his car is an NCS as well.

Hayden, I will share with you what all I've done in a bit.

So on this 2013... which is a CJAA+DSG car, it is all stock. It had a previous repair of some issue with the glow plugs, that ultimately ended up requiring a new engine harness which was poorly installed by another shop. It did fix that problem, for a short time, and then something else came up and that shop didn't want to mess with it anymore so it ended up here.

First thing I found, is in addition to the P0651 DTC, it also had a handful of other seemingly unrelated DTCs, some of which I don't remember but I did jot down a P0470 (exhaust pressure sensor 1), P2452 (exhaust particulate filter sensor), misfires P0300-04. There were some others, I don't remember. I immediately noticed the awful engine harness install, it was all routed wrong, and the left cooling fan and ground a big chunk through it. The car did start and run, but it had a long crank time, flashing glow lamp, unsteady idle, and reduced power. The harness was SO mangled, and without even investigating it much further, I went ahead and ordered another new harness... I honestly thought that would be the whole deal.

Installed the new harness, correctly this time, reconnected everything, didn't see anything else amiss, turned the key on, cleared the DTCs, started the engine. All the other DTCs remained gone, but the long crank, flashing glow lamp, and the hard P0651 remained.

What I have found:

The 5v reference wires (two of them) that come from the car-side ECU connector (T94) not the engine side ECU connector (T60) which is the end of the engine harness I just replaced, have only .55v on them. These are pins T94/17 to the G31 MAP sensor, and T94/15 to the G79 accelerator pedal position sensor #1. The MAP is integral with the IAT, G42, and uses four wires that come out of the ECU and go down to a 4-pin connector, T4aj, that clips to a bracket attached to the M-unit's cover, that then goes into the same sub-harness that the alternator and compressor wires use. The pedal sensor 1 is integral with pedal sensor 2, G185, and go directly from the T94 ECU connector to the main harness and into the dash area and straight to the pedal assembly, no connectors in between.

Unplugging the T4aj connector changes nothing other than it does induce a DTC for the IAT. Unplugging the accel pedal changes nothing other than it does induce a DTC for the pedal sensor 2.

In the measuring blocks, the value for the MAP is stuck at 2190 mBar, it never changes... KOEO or KOER, doesn't matter. Stuck there. Same goes for the #1 pedal sensor. Stuck at 0.00v, never changes, you can move the pedal down and up, nothing. #2 value changes normally as you'd expect.

So the ECU is not putting out the required 5v on either of these legs. I assume that these are the "B" reference circuit, but none of this is actually labeled.

I tore the harness apart enough to isolate the paired wires to the T4aj connector from the T94 connector, and they are good. I checked from the T4aj to the MAP/IAT itself, and they are good. No blown fuses found anywhere, nor any missing fuses. The main power and ground wires to the ECU, all in the T94 connector, are all doing what they are supposed to do.

Some other odd things I found in the measuring blocks:

Group 054, Block 2, reads a randomly changing RPM... KOEO or KOER. Not sure what that is, and it may be normal.

Group 013 Idle Stabilization... all blocks 0.00. Never change, running or not.

Output Tests: neither EGR valve seems to work, but never sets a DTC. These are a little difficult to unplug, but you should still here them sweep, especially the upper one (the throttle valve and the intake runner Output Tests run normally and you can hear them fine). The N75 Output Test will also not work. The power side is there, but the ECU is not grounding the other side. It WILL set a DTC for it if I unplug the N75, but with it plugged in it will not operate it, and will not set a DTC.

I feel like the ECU is not getting something... a power or ground... but I cannot figure out from where.

I plugged in a known good CJAA ECU, and aside from the expected DTC for immobilizer block, it does the exact same thing. I checked another identical car I had here, and there are 5v reference on both those 15 and 17 T94 pins.

Also, when this engine is running, it seems to have a slightly uneven idle, almost like what they do when they are in Basic Settings mode, but without the increased RPM.

I also checked the ground points to the body under the left headlamp, which are where all the ECU grounds originate I believe. I also looked over and made sure nothing else was out of place, and the N75 and PCV heater connectors are not swapped, and I checked the integrity of the harness above the right belly shield that goes to the exhaust bits in the middle of the car and that is all secure and clean. Checked as best I could under the dash, and wiggled things around, nothing found there either.

I quickly skimmed over your post and noticed you said the T94 is part of the car-side harness and that you checked over the grounds near the headlight. I looked up the T94 harness and found it says there is ground connections by the Plenum Chamber, Left. Not sure if you have checked this and I missed it in your post. But here is a screenshot if what I can find.

Different car. This is an NCS. That's an A5.

Ah gotcha, my bad!