gb944

Hello, All,

Having a strange problem with my 2001 A6 2.7T.

MIL for codes equating to B1S2 and B2S2 oxygen sensors internal resistance too high. After replacing both sensors with the factory sensors and verifying that they are plugged in correctly and in the correct side of the exhaust, still throwing those fault codes.

So, spent quite a while with VagCom (thanks Uwe!) and for measuring blocks 041 and 042, the resistance reported by the ECM is 25.50 Kohms for the heater circuit on those two sensors.

So, using a ohmmeter, tested the circuit from the fuse (which supplies 12.9 vdc) to the pin on the ecu (63 or 6 respectively) and they measure 13 ohms when cold...

So, my question is: Is it likely that the ecm is bad and reporting only that fault falsely?

Is there a way for me to reset the ecm to report it correctly, or do I have to now find a ecm to test my theory?

Thanks in advance...

George B in Upstate New York

PSUEng

I would check the resistance of the heater across the wires on the sensor itself. I used to work for an O2 sensor company. Try that. 25.5 kOhms sounds about right.

gb944

Already made that measurement... as I noted in the first post, the resistance of the entire loop, including the harness is 13 ohms... quite a difference from the 25,500 ohms that the ecu is reporting...

I'm just wondering about the plausibility that the ecu is bad...

Thanks for the response...gb

Uwe@Ross-Tech.com

Sepcified value for heater resistance is 0 - 0.5 kOhm, with the note: "It can take a few minutes until specification are obtained".

Source at link below.

-Uwe-<ul><li><a href="http://ebahn.bentleypublishers.com/audi/servlet/EbahnReq?action=Goto&amp;type=repair&amp;id=AUDI.C 5.FU03.24.2.111.5">Oxygen sensor heater for oxygen sensor, checking</a></li></ul>

gb944

Thanks, I already have that information, and it is correct.

Since the heater wiring is within spec, and the ecu is reporting it as 25.5 Kohm (according to the vagcom), would it then make sense that the ecu needs to be replaced, or should I look elsewhere outside the ecu?

Thanks for your help...

gb

gb944

Replacing the ECM fixed the CEL and is now reporting the 02 Sensor Heater Resistance correctly.

Thanks for your help. I could not have diagnosed the problem without the Vagcom and the Bentley Manual.

gb