TDI Injector: Caddy CFHF, 2.0L, P0641

Hello everyone,

I'm having the following problem after replacing the EGR valve:

4123 - Input reference voltage 1/A.
P0641 00 [167] - Interruption.

Background:
After the EGR valve failed, I replaced it. During the repair, it appears I damaged one of the exhaust temperature sensors on the particulate filter, as we didn't remove it, but only pushed it to the side.
Error:
The preheating indicator light usually illuminates after turning on the ignition, but it goes out after 1-2 cycles of turning the ignition on and off. Occasionally, after a cold start, the engine power suddenly drops significantly, and the indicator light comes on. After turning the ignition off and on (while leaving the gear in the same position), it runs normally again. The same error message is always stored in the error memory. I have recorded sensor readings during several trips related to the exhaust aftertreatment system, and I have not detected any inconsistencies. All the signals appear to be normal. No sensor signal is interrupted or anything like that.
As a precaution, I once filled up with expensive diesel to avoid overworking the particulate filter.

Can someone in this forum explain the error message in more detail? What exactly is the voltage? Does the ECU measure the voltage back? It seems that the sensors have a common return line. Shouldn't all the sensors fail simultaneously then? I've also tried gently pulling on the cables while the engine is running (but cold), but I haven't been able to trigger the error.

Have a great weekend!


VAGCOM displays the following message:

Address 01: Engine Control Module
Label file: DRV\03L-906-018-CFF.clb
Control unit part number: 03L 906 018 NF. Hardware number: 03L 907 309 R.
Part and/or version: R4 2.0l TDI H25 9978.
Encoding: 00190012040400080000
Operating number: WSC 41078 001 1048576
ASAM Dataset: EV_ECM20TDI01103L906018NF 003004 (VN35)
ROD: EV_ECM20TDI01103L906018_003_VW36.rod
VCID: 7BFE3394F2C3B397CC-802E
"One error found:"

4123 - Input reference voltage 1/A.
P0641 00 [167] - Interruption.
Warning light ON - unconfirmed - checked since last reset.
Environmental conditions:
Error status: 00000001
Error priority: 2
Error frequency: 11
Mileage: 116,036 km
Date: 2000.00.00
Time: 00:00:00

Motor speed: 0.00 rpm.
Normalized load value: 0.0%
Vehicle speed: 0 km/h
Coolant temperature: 15 °C
Intake air temperature: 11 °C
Atmospheric pressure: 970 millibars.
Voltage at terminal 30: 12.180 V.
Lost learning counter via OBD: 40.
Exhaust temperature sensor 1: 20.0 °C
Exhaust temperature sensor 2: -0.0 °C
Exhaust temperature sensor 3: 55.5 °C
Exhaust temperature sensor 4: 22.3 °C.
Timer: Last engine shutdown time: 5147 seconds.

Attached is the error again, as it occurred at a different time.

It sounds like a sensor is drawing too much current, which is causing the voltage to drop. I would start by disconnecting each of the sensors, starting with the one that is suspected to be faulty, and see which one, if any, causes the error to disappear.

Possibly, the new AGR (Arbeitsgemeinschaft für relevante Themen) is also to blame.

Quote:

It sounds like a sensor is drawing too much current, which is causing the voltage to drop. I would start by disconnecting each of the sensors, starting with the one that is suspected to be damaged, and see which one, if any, causes the error to disappear.

I had also considered that. However, the problem would then be that the engine would go into a limp mode, which would then cause other problems. I would need to record the voltage. Perhaps the interruptions are so short that the VAGCOM doesn't detect them.

Quote:

The problem would then be that the engine would go into emergency mode, and that would then cause other problems. I would need to record the voltage.

It doesn't really matter for testing purposes whether the system goes into emergency mode or not, or how many other errors are stored, but rather whether and when the aforementioned error no longer appears.

I don't know what you've tinkered with, or which components or wiring harnesses may have been damaged. Therefore, I would personally start with your first assumption (the sensor), followed by the new EGR valve. If it's a cheap product, that's not out of the question.

You simply need to start with basic logical searching.

Thanks for the tip! I've taken a slightly different approach, and unfortunately, I haven't found the error yet.

Ich habe an den Kabeln zu den Abgastemperatursensoren neben den Steckern an der Spritzwand Abgreifklemmen mit Schneid-/Klemmtechnik ("Stromdiebe") angebracht und ein mobiles Oszilloskop angeschlossen. Man sieht (Zündung an) zunächst mal eine konstante Spannung von 5V. Die Triggerung habe ich dann auf etwas unter 5V und abfallende Flanke gestellt. Als ich an den entsprechenden Kabeln, Sensoren usw, wo man eben hinkommt gewackelt habe, hätte ich auch einen sehr kurzen Einbruch der Spannung sehen müssen. Den Test habe ich reihum bei den Sensoren gemacht, im Stand und bei laufendem Motor. Nnothing...

Before I continue searching, I wanted to ask in the forum if it's possible to extract more information from the error message.

4123 - Donor reference voltage 1/A.
P0641 00 [167] - Interruption.

What does 4123 specifically mean, and what does P0641 00 [167] mean?

I would like to narrow down the search as much as possible, as it's also nice to have access to everything. Which sensors are connected to the reference voltage? Is there a schematic diagram of the control unit? ... I was somewhat surprised during my search that no one (has publicly) reverse-engineered it.

Quote:

Is there a schematic diagram of the control unit? I was somewhat surprised during my search that no one (has publicly) reverse-engineered it.

Not only you...

According to a reliable source, the following sources of error are known, or have led to solutions:

- Differential pressure sensor... even though it may appear to show plausible values, it was...
5 cases defective.

- AGR valve... was defective in 2 cases.

- Cable harness to the accelerator pedal sensor chafed through near the pedal assembly... 1 case.
known.

Instead of drilling through the wiring harness, as mentioned earlier, you should start with the simple things and disconnect any potential sources of error from the circuit.