Hey all, I am chasing a P0131 / 2D00. The car runs fine besides the higher fuel consumption. ISTA & INPA says it’s a short to ground from the signal wire of the precat O2 sensor. What’s strange is that the dtc get’s set as soon as I turn on the ignition (CL15 only).

Is anyone familiar with this issue and maybe can give a hint on what I may have missed?

What I did so far:

• continuity & resistance check of all wires from precat O2 Sensor Plug to ECU - all good
• continuity test against ground wire - no short
• replaced precat O2 Sensor with OEM one’s (2x)
• read out sensor values while driving are barely changing: 1,49-1,5v @ lambda* 0,99-1,0

I assume that it might be an issue with the ECU?
Cheers

 

Do you have the Hex DTC code? If its the pre-cat sensor, I would expect 2A99, or something... The Hex code will help narrow down the issue. The Pxxx code is a little bit generic on these cars.

 

Yes it is the pre cat sensor (2D00 - will edit the post above).

Cheers

 

If you checked the harness from the DME to the sensor, and replaced the sensor, maybe there is a harness abrasion that is causing an intermittent short to ground? My last guess would be an internal DME fault.

 

Hmm could be...I will test the harness again but this time under load (test lamp & multimeter).

What I dont understant is that the DTC get's stored directly with CL15 ON...I always thought that this would happen only when the ECU is trying to get into closed loop.

 

Update: While testing under load I could see a voltage drop...found a spot where the insulation was worn. Fixed the wire and now everything works fine.

So from now on - I will always test the harness under load.

Case closed