Someone contacted me about his V10 Audi S6 that had almost $8000 spent on it by the local European car specialists. The main issue was that it would go into ‘limp mode’ or totally shut down with acceleration or deceleration occasionally. First they told him it needed new intake manifolds due to a fault code for the intake manifold runner flap fault codes. $3k later and as he drove away it happened again. They told him “That’s a different fault, we fixed the original fault”. Then it needed two new throttle bodies…. $8k later and several visits with the same reply each time and he wasn’t going to return there. Due to the busy time of the year I loaned him my VAG401 and it cleared the fault perfectly each time it happened.
Part of our conversation went like this:"Basically the steering column lock is making it so the ignition etc is off, so the scanners won't connect"
"The steering column lock actuator module (J518) fails, it's a common Audi A6/S6 etc issue, I've read up on how to disable it permanently but my electrical skills aren't good lol" and he supplied a video link https://www.youtube.com/watch?v=ujxQLU_ ... cODvbuP_ao which shows a procedure for waking the car up after it has died. Turn on park lights, hazards, high beam and press brake, then you can scan it.
Apparently it brought up a 00288 fault code for the steering lock actuator. It never did it for me but the EPC light and traction control light stayed on and though it is a 5.2l V10 quatro, flooring it takes revs to 3000 rpm and it slowly increases speed and battles to get to 60km/hr, it also had a slight misfire.
The codes I had were:
ECU: 5715 "read dtc of ABS"
1431 "thermostat heater control circuit"
6435 "check dtc memory of ECM 2"
ABS: 1826 "SAS voltage supply"
1314 "ECM read dtc"
The customer who had spent months trying to solve the issue provided a link - see #13 https://www.audiworld.com/forums/a6-s6- ... 537/page2/
Also I managed to scan ECM2 and found fault codes for implausible sensor readings from both throttle bodies and cleared them. I then found that if I wriggled the wiring going to the left throttle body the revs suddenly surged and cut back after a few seconds. Since he said it only did it on acceleration it made sense that the twisting of the engine caused the miss-reading at the throttle body sensor when the harness moved and the vehicle shut down because of some sort of logic error. Regardless of the many forums suggesting replacing the steering assembly to fix code 00288 it made more sense that the code was a result of the throttle body fault causing some sort of shut down of the system. This is an oscilloscope pattern of the position sensors on the left throttle body. Two opposing sensors that always add up to the same number so the computer can be sure the signals are ‘normal’. If something goes wrong like perhaps one sensor losing its ground, and it outputs 5v all the time then the two signals added together will go higher than what the computer expects and it will give a fault code, and in this case go into limp mode - possibly also resulting in the steering lock fault
Since the engine misfired when the left wiring harness was moved I removed the left throttle body and gave the pins each a 'twist' to make better contact with the terminals and put it back together, as a test. Lots of test driving later and the problem seemed to be solved. The vehicle was returned to the customer for testing as a more economical option than paying us to drive it till it failed, and it went well for a week before doing it again. The vehicle was brought back in again and the terminals were soldered directly to the pins of the throttle body which fixed the fault permanently. Audis faults aren’t exactly logical - the repair will get very expensive if you replace everything that shows a fault code.
