A6 (C7) - 2.0T - P0140 fault - O2 Sensor Circuit

[Wberner]

Hello All,
First new thread from me.* I searched the forums, but haven't been able to find anything yet for this problem, so I thought I would start a new thread.* Also, I have a 2014 A6 (C7) - 2.0T.

A few months back, I had to disconnect my rear O2 sensor connector in the engine bay and when I reconnected it, the MIL came on and it was showing a P0140 fault - O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 2).* I continue to get this fault no matter what I do. My OBD 2 can read the voltage from the O2 sensor in question and it is consistently reading 0.52-0.53. So the fault is legit. Just can't seem to figure out what is causing it. This is what I have done so far:

1.*I have changed out the O2 sensor (twice) - Brought an aftermarket first and then tried an OEM sensor.
2. I changed the O2 sensor connector (on the car side) to make sure it wasn't due to damage that may have been caused when replacing the sensor
3. I cleaned my MAF.
4. I changed (ALL) the fuses in the engine bay fuse box, just in case.
5. Disconnected the battery for 15 mins and reconnected.

NOTE: I cleared the code after each fix and the fault continues to come back.

Has anyone else ran into this issue?* Any help would be greatly appreciated.

Thanks,
Wade

[gk1]

What specifically are you using to clear the fault?
VCDS
OBD11
Something else?
Are there no other faults in any other modules?

[Valpo A7]

How is the engine running, hows the power and fuel economy?

I googled the P0140 code and it points to a problem with either the O2 sensor or the MAF. Test the MAF and see if its getting the proper readings. Worst case is to replace the MAF if the O2 sensor has been changed and still has problems.

What repairs can fix the P0140 code?
After scanning and clearing all fault codes and verifying the failure:

Test the O2 sensor to see if it changes when the fuel mixture is enriched
Test the mass airflow sensor for the proper readings per specifications
Replace the O2 sensor if contaminated or fails tests
Replace the mass airflow sensor if contaminated or fails tests
Clean out the mass airflow sensor to see if readings change

Additional comments for consideration regarding the P0140 code
The no response of an O2 sensor may be due to a mass airflow sensor that is contaminated from things like oil from an oil impregnated air filter, as is common to all sensors. This oil coats the sensor and can cause it to become inaccurate. Cleaning the sensor may or may not fix the problem.

[Wberner]

Thanks for the quick response...
gk1 - I am using an OBDII to clear the fault. No other faults are coming through.

Valpo A7 - Engine runs completely fine. No indication of an issue. I did clean the MAF with the proper cleaning spray but no luck. I will try and get MAF readings tonight.

[gk1]

Thanks for the quick response...
gk1 - I am using an OBDII to clear the fault. No other faults are coming through.

Valpo A7 - Engine runs completely fine. No indication of an issue. I did clean the MAF with the proper cleaning spray but no luck. I will try and get MAF readings tonight.

Is it just a generic OBD2? or do you mean OBDeleven?
Perhaps see if you can find someone with a latest version VCDS who can try clearing it for and see if that helps.

[Wberner]

I have a couple simple OBD2 devices (Actron PocketScan and a cheap WIFI one).

The fact that the voltage is not changing for the O2 sensor makes me think that it is more than an uncleared code. To make it more confusing, I was able to check the MAF readingsand they seem good (idle is about 6 g/s or 0.6 lb/min) and it adjusts with the revs, unlike the O2.

Not sure of anyone around me that may have the VCDS to clear it, but I can see if that would work.

[gk1]

Well unfortunately since you replaced the sensor multiple times, checked and replaced the wiring and nothing is still working correctly my only guess left would be something amiss with the ECU.

[Ryanhouck9]

I have a couple simple OBD2 devices (Actron PocketScan and a cheap WIFI one).

The fact that the voltage is not changing for the O2 sensor makes me think that it is more than an uncleared code. To make it more confusing, I was able to check the MAF readingsand they seem good (idle is about 6 g/s or 0.6 lb/min) and it adjusts with the revs, unlike the O2.

Not sure of anyone around me that may have the VCDS to clear it, but I can see if that would work.

Hey did you ever figure this out?? I have the same issue with my 2016 s6! Replaced both sensors too…


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