I got a check engine light the other night when i was going down the highway and checked it with my vag-com and P0140 was the only code that came up nothing pending, i replaced both o2 sensors when i put in my test pipe 3 years ago and i did the spark plug non-fouler trick and never got any codes from either o2 sensor till the other night. i have searched here and on another forum and only found only posts with P0140 included in a list of codes with other issues and not just P0140, is it just a fluke that it poped up or could it be something else going on???

 

Use the VAGcom or a DVOM to check the voltage of the post-cat O2 sensor when hot. It should be about .4-.5 V (.2-.9 min-max) If there's no signal, check the resistance of the wire from the ECM to the O2. If it's less than a few Ohms, your O2 sensor might be dead. Swap it out and compare signals.

If the code returns, you'll likely need a new ECM or you need to dig deeper into the wiring harness to look for damage.

The reason most others see codes with P0140 is due to a bad heating circuit. The O2 sensor doesn't heat up and wont send a voltage signal to the ECM. It's also a possibility the heating circuit is bad, so check the resistance on the wires going to the O2 sensor while you're investigating the ECM harness.

 

should i be looking at the pre cat or the post cat 02??

 

P0140

O2 Sensor Circ.,Bank1-Sensor2 No Activity Detected

Post-cat O2.

 

so could that be from my test pipe with the post cat o2 spaced out???

 

Yes. But you have to make sure the sensor is working. A sensor detecting atmospheric O2 will still be sending a signal of some sort. You have no signal.

 

I just scan my audi s4 b5 today with the AutoScaner Plus
And i have this codes..
P0140 , P0141 and P0431 can anyone tell me what i need to do to remove this codes?..