A3 Engine Management diagnosis Enquiry


New Member
Jun 3, 2021
Reaction score
Good Afternoon All,

Wondering if anybody else could help me diagnose an issue with my partners A3.

So, in October 2021 the EML light came on and the car went into essentially limp mode and wouldn't rev past a certain point. I managed to read the code with Torque GT and it turned out the issue was the throttle pedal, so I ordered a genuine Hella unit, swapped it out and jobs a goodun! Car drove perfectly.

October 2022, partner was on her way home and drove over a speed bump just around the corner from our house and the EML popped on again. The car drove no differently, no limp mode, no nothing. Plugged into the car again, using Torque GT and had a similar code, if not the same code. So, I cleared it and off she popped again, no return for a week or two. Anyway, a friend of mine has the proper VAG software for code reading and we plugged it in yesterday. The only code stored was P0121, which was stored 6 times since October 2022, which co-insides with the light coming on in the first place.

Google that P0121 code and it talks about Throttle body cleaning... which it can't be with it being a diesel. Anyway, we ran the software and then decided to see what the throttle values were. Gradually adding pressure to the pedal, we watched the value creep up 1% at a time (for both readings A and B). Then at about 31% on A, B dropped out to 0% until more pressure was applied and then B dropped out again at 42%, 61%, 72% and 80%.

We tried again with the car on this time but it didn't flag a code, which we guessed is because it drop out long enough for the ECU to class it as a detrimental fault. We then turned the car off and the code flagged again and the car shuddered on shut down. Now it has been doing this (shuddering) from owning the car but only intermittently, I've found it only does it if you don't put the clutch in but that could be pot luck, I'm not turning it on and off for 10minutes to find out. We cleared the code and did the same thing, upon turning the car off EML again. So we think it could be the Shudder Valve and because it's going to be gunked up after 94k, the cars unable properly find the correct position for shut off and this is the cause of our EML.

So, has anybody else had this, fixed this or have any suggestions. P0121 is ridiculously vague as a code, when you search online.

5286 - Throttle Position Sensor (G69)
P0121 00 [237] - Implausible Signal
MIL ON - Confirmed
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 6
Mileage: 146034 km
Could be a faulty pedal.
It could be, but I highly doubt two faulty pedals, the last pedal was knackered (factory fitted) and wouldn't allow the car to rev past 30%. This pedal has worked with no issues, seems a little odd the code only throws on shut down, no? I'm not fully dismissing it, but I highly doubt that's the issue, I just felt it was necessary to mention it. It isn't throwing a code when "Value B" drops out for 0.005 of a second, just on shut down when it shudders. Which then makes it more obvious that's the issue but I want to look into it more and see if anybody else is having/had this problem.

Also, the fact it's happened 6 times since October, think how much use that pedal gets over a 20+ mile commute and the range it's going through, on the motorway and through a city.
Spent an hour and half giving the inlet throttle valve a light clean...

20230112 120928
20230112 120933
20230112 125048
20230112 125110

The car now drives faultlessly. Took the car out for a long drive so it got up to temp, mixture of average road speeds and then duel carriage way and motorway. Turned the car off before returning home and it turned off clean with no judder at all. Rescanned the car, no codes whatsoever and then fired it up to return home. Quite a simple job, shame my hands dont illustrate that now but it's a job I'd recommend is undertaken on any diesel close to 80k, never mind 90.