Audi A6: AFN/WFS Problems - Common Issues & Fixes

Strange: AFN 01262 and WFS issues with Audi A6, 4B.

Hello diesel enthusiasts,

I am experiencing the following problems with my Audi A6 AFN, manufactured in 1998:

Before my vacation trip, the car wasn't performing well; it was running like it didn't have a turbo.
The problem was a torn vacuum hose on the turbocharger and a damaged cable to the N75 valve (magnetic valve for boost pressure control, turbocharger). The hose and cable have been repaired. During a test drive, the Audi ran perfectly again.

"As we were about to leave, the car wouldn't start. The starter motor wasn't engaging. I suspected a problem with the immobilizer (wiring connection, sensor, etc.). I tapped lightly on the ignition switch several times and adjusted the steering wheel up and down. > The A6 started. With a slightly uneasy feeling, I then drove 850 km without any problems. During the vacation, the car would consistently start on the second or third attempt and ran perfectly. > This obviously can't continue like this. Today I'm back home. In total, about 2000 km were driven."
"I just read the error memory and surprisingly only found error code 01262: 'Solenoid valve for boost pressure control N75, 31-10 open or short to ground - intermittent.' So, it's that solenoid valve. However, the car is running perfectly fine. This error message reappears immediately after clearing it and restarting the engine (idling only)! I checked the valve according to the workshop manual: The resistance between the two contacts is 16 ohms, which is within specification!"
The repaired (soldered) connection is also working properly, unless there's a really bad "intermittent fault" that I didn't notice while testing.
Here's the first question: What is the resistance (with the ignition off) measured between terminal 1 and terminal 2 on the cable?

Surprisingly, I don't find any error codes related to the reading coil, key, WFS (signal too weak), or anything similar in the fault memory.
Actually, the two errors (starting problem and solenoid valve issue) probably aren't related to each other... or are they?
Could this be the much-discussed relief relay (which would likely be number 100 or 219 in my case)?
How can I check this?

Best regards,
0928-761

Hi.
The WFS is not your problem!
If it starts, the engine kicks on and then turns off again after about one second.
You seem to be encountering a more fundamental problem in the area of power supply/connection for the MSTG (Multi-Sensor Test Gauge).
to have.
A faulty 109 often leads to the funniest error messages – although, more commonly, it results in different .
The relays in the A6 are located near the steering column, which could cause slight vibrations.
Can the ignition switch also be transferred there?
Then you should definitely thoroughly examine the relay (or replace it immediately, or resolder everything).

Best regards,
Rudi

I have now checked various relays and wiring, and everything seems to be fine...

Could it be that the magnetic switch on the starter motor is sticking - occasionally?
Because: after approximately 3 seconds, only the battery indicator in the instrument cluster lights up, so everything is as it should be.
Has anyone here ever replaced this part before?
What problems occurred back then?

The error code "Magnetic valve, boost pressure limiter" would not be related to the occasional starting problems.

Best regards, 0928-761.

0928-761 wrote:

Could it be that the magnetic switch on the starter motor is sticking - occasionally?

Yes, that could be it. However, it might also be due to the ignition switch contact set, which sometimes fails to send power to the starter motor. Or there could be a loose connection somewhere between the ignition switch and the starter motor.

Is your problem only that the starter motor occasionally stops working, or does it also sometimes crank normally (as it should), without the engine starting?

Quote:

The read error code: "Magnetic valve, boost pressure limitation," would then have nothing to do with the - occasional - starting problems.

Okay.

No, the starter motor never just whirs. When it starts, it always does so immediately with the ignition key – or, alternatively, it makes absolutely no sound at all .

Best regards, 0928-761.

0928-761 wrote:

No, the starter motor never just whirs. When it starts, it always does so immediately with the ignition key - or it doesn't make a sound at all.

Then the problem lies somewhere between the ignition switch and the starter motor (unless all the lights go out when it doesn't start, in which case it's likely the battery or the wiring around it).
Small consolation: because of this defect, it will never unexpectedly run out on you, and if necessary, it can also be pushed/towed/rolled .

Thanks, Ulf! That sounds logical and fits with the observed problem(s).

I will now try to narrow down the error to one of the two components or their connections.
If anyone has a practical tip to share, please feel free to do so.

The problem is that it's very difficult for me to access the starter motor itself for measuring purposes...

Otherwise, I'm going to have to struggle through the wiring diagrams now.

Mfg 0928-761

Hello diesel enthusiasts,

This afternoon, I replaced the ignition switch (24 euros) because everything was already disconnected for testing. On the Audi A6 (C5, 4B), this is only attached to the ignition lock with two set screws.
A laborious process of removing a sleeve, like in golf, was not required.
The problem with the occasional non-starting issue persists.

Okay, so I'm going to focus on the starter now.

Best regards, 0928-761.

Okay, here's the final part of the project:

It was the magnetic switch (available separately for €39 including shipping on eBay!) of the starter motor! However, when ordering, you need to know the manufacturer (in my case, it was a "Valeo") and the OEM number "068911024E" of the starter motor. You could barely read it from above using a flashlight.

Now the Audi starts reliably again.

To the admin:
The topic doesn't fit into this subforum anymore. > However, I couldn't have known that beforehand.

Best regards from 0928-761.


P.S.: The error code "Boost Pressure Control N75" was caused by a poor pin connection... However, the car always ran perfectly fine. It's usually those small things that cause all the trouble...