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Hi All

I'm reaching the conclusion my ABS module is toast and would appreciate any ideas on anything else I could check before booking her in.

Symptoms - for the last few weeks I have been getting the ESP warning light or ABS light illuminated (never both at the same time). Typically when I start the car no warning lights are displayed, then after a few miles the ESP light comes on and after another few miles it will go out but be replaced by the ABS light or vice versa. Turning the ignition off usually clears this.

I've also noticed that the car feels down on power when the ABS light is on but fine when the ESP light is on/no lights are on. So far I've fitted a new brake switch, cleared codes and scanned again, the codes below have been returned. I should add that when I tried reading module 03 ABS when the ABS light was on last night it could not see the controller, but when I've scanned with no lights or ESP only it can.

A few questions:
1. I'm going to try cleaning the ABS module and yaw sensor contacts- is the yaw sensor under the rear seats (avant)?
2. Can I pull the ABS fuse and drive the car without it?
3. Has anybody used http://www.ecutesting.com to rebuild their ABS module or recommend a similar company?

TIA

Chassis Type: 4B - Audi A6 C5
Scan: 01,02,03,06,08,15,16,17,18,22,34,35,36,37,45,55,56,57,65,67,75,76,77

-------------------------------------------------------------------------------
Address 01: Engine Labels: 077-907-558-BCY.LBL
Controller: 4D1 907 558
Component: 4.2l V8/5VT G 0002
Coding: 0010752
Shop #: WSC 66565
VCID: EBA9C4AF8A9D
3 Faults Found:
18057 - Powertrain Data Bus: Missing Message from ABS Controller
P1649 - 008 - Implausible Signal - Intermittent
16502 - Shareware Version. To Decode all DTCs
P0118 - 002 - Please Register/Activate - Intermittent
16955 - Shareware Version. To Decode all DTCs
P0571 - 008 - Please Register/Activate - Intermittent
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: 01V-927-156.LBL
Controller: 4B0 927 156 FB
Component: AG5 01L 4.2l5VT RdW 1315
Coding: 00001
Shop #: WSC 00000
VCID: 6CAB47B30F93
1 Fault Found:
17087 - Brake Switch (F): Electrical Malfunction
P0703 - 35-10 - - - Intermittent

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 4B0-614-517.LBL
Controller: 4B0 614 517 AD
Component: ESP 5.7 RS 6 2310
Coding: 06697
Shop #: WSC 02195
VCID: 63B92C8FE24D
2 Faults Found:
01425 - Yaw Rate Sensor (G202); Signal Wire
57-10 - Electric Circuit Failure - Intermittent
18256 - Shareware Version. To Decode all DTCs
P1848 - 35-10 - Please Register/Activate - Intermittent

Your coolant temp sensor is giving errors. You should change this as implausible values from it can mess with the mixture and that can mess with the engine torque calculations which can put the ABS / ESP lights on.

Also, that yaw sensor thing is weird. Does it come back if you clear it?

Thanks for the quick response! I'll get the coolant temp sensor replaced, exactly where is it located? Re the yaw sensor yes it came back after I cleared the codes. Am I right in thinking it is located under the rear seat in an avant?

Pretty sure it's under the bench seat. Might be worth checking the wiring and connectors before getting a new one. You might even be able to pull it apart and resolder it if you are feeling adventurous (and don't mind the extreme high likelihood of binning the sensor afterwards).

The coolant sensor is down the back of the engine on the left hand side (from driver's POV). Green sensor. Plenty of threads on here about it.

I had an error from one of my YAW sensors once. Unplugged it and WD40 the joint and the error never came back. They aren't that expensive and I think they are fairly common across the Audi range.

Yaw sensor under the rear bench, same on the allroad etc ,

Just got rid of my ABS module problems before AITP8 and mine was the ABS module and seems like it's cropped up a few times recently on other owners cars. Maybe it's the age of the circuit boards? Have to say mine only kicked in after a bit of driving plus it seemed down on power so I was glad it wasn't a mechanical issue in the end.

A belated update after picking my 6 up yesterday. Having fitted a new brake light switch and /checking cleaning the ABS module, yaw sensor connections, fuse, etc I was still getting the following codes along with intermittent ESP or ABS light:

18057/P1649/005705 - Powertrain Data Bus: Missing Message from ABS Controller
16885/P0501/001281 - Vehicle Speed Sensor (G22): Implausible Signal
16955/P0571/001393 - Brake Light Switch (F): Implausible Signal
16502/P0118/000280 - Engine Coolant Temperature Sensor (G62): Signal too High

Car went into a local VAG specialist who confirmed ABS module failure and I arranged for the unit to go to http://www.ECUtesting.co.uk for rebuild, see link below for C5 RS6 module.

http://www.ecutesting.com/catalogue/aud ... &model=824

I also had the engine coolant sensor replaced whilst the car was in.

Although it's early days the car is code free and back to it's normal self! For the cost compared to a new ABS unit £1K+ I'm very pleased with the result and the service/communication I received from ECUtesting. Hopefully other people will find this useful as it appears age/mileage related i.e. the ABS circuitry degrades over time. FWIW my 6 has just clicked over 115K.