Hello

Please help. I have a 2003 A4 B6 with a 2.4 V6 petrol engine (ADV). It has been running slightly lumpy for a while - especially when cold and intermittent MIL on/off.

VCDS has reported 4 faults as shown below.

4 Faults Found:

17537 - Fuel Trim; Bank 2 (Mult)
P1129 - 002 - System too Rich
17535 - Fuel Trim; Bank 1 (Mult)
P1127 - 002 - System too Rich - Intermittent
16518 - Oxygen (Lambda) Sensor B1 S1
P0134 - 004 - No Activity - Intermittent
16538 - Oxygen (Lambda) Sensor B2 S1
P0154 - 004 - No Activity - Intermittent

I have done 160,000 miles in the car and it does run ok - especially on the motorway. If I am driving locally i.e just a few miles a day, then the MIL will come on. If I am driving on the motorway (which I do quite a bit) around 200 miles in a day, then the car runs fine.

Does anyone know a common problem to these engines that I could look for, as I would prefer not to pay dealer prices for diagnosis?

Many Thanks
Steve

 

All of those codes point directly or indirectly at your primary (pre-cat) O2 semsors being bad. I would start with those.

 

Hi

Is there any other checks I can do with VCDS to show whether both o2 sensors have failed or whether it is only one?
Many Thanks
Steve

 

Yes, this could be due to an O2 sensor failure, but it's kind of unlikely that both failed at the same time. With VCDS you should be able to see the real-time O2 sensor signal. It fluctuates all the time, so you probably won't be able to see anything interesting there, but at least you'll see if it gives ANY signal. If either of the sensors is stuck at the same value for more than a couple of seconds, it's bad. The system normally adjusts many, many times per second and each iteration leads to a slightly different read from the O2 sensor.

Another possible (and in my mind, more likely) reason is a bad or dirty MAF sensor. Try cleaning it with MAF cleaner spray. Also check its electrical connections, make sure the plug is firmly plugged in, the wires are not torn/damaged, etc. The MAF may seem unrelated to the error codes above, but in effect, the computer decides how much fuel to spray in the engine based on the signal from the MAF (among others). So if the MAF is giving it an incorrect reading, the computer may be putting in too much fuel, leading to the "rich" condition in your error codes, which is detected via the O2 sensors.