Bradfr

I recently bought a car that had a p0161 error code that refers to the heater circuit failure on bank 2 sensor 2. From what I read this was the driver side post cat sensor. I have replaced that sensor with an OEM sensor, cleared the CEL and I still keep getting the error coming back. I followed the wires back to the fuse box under the hood and it appears to be in good shape. Any ideas why this might be coming back? Did I maybe replace the wrong side? The second time I cleared the code for p0161 a p0400 came on. Is that perhaps the issue that is causing the p0161 error or vice versa?

Glyn M Ruck

P0161 = O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
P0400 = Exhaust Gas Recirculation Flow Malfunction

You have replaced the correct sensor. Check out the EGR system. The EGR system playing up can give you a high reading on the post Cat sensors but not a heater malfunction.

What mileage is on this car. It might be time for new O2 sensors all round.

Bradfr

The car has 130k miles on it. I would think if it were time for all 02 sensors that the others would be throwing a code as well no?

Glyn M Ruck

You are getting into the window where O2 sensors could be cycling too slowly.

Your recurring 161 makes no sense if the new sensor is good & a proper Benz heated sensor.

Bradfr

This is the exact o2 sensor that I bought to replace the one that was not working.

Is this not a proper Benz heated sensor?

Glyn M Ruck

That is the correct sensor. Darn good price. I hope they have their equivalents correct. Picture & OE P/N is correct. Is what you received indentical to the picture including the 4 pin connector? Excuse the questions but universal sensors always give trouble on Benz.

Here is RM European listing for your car.

Bradfr

Yes, what I received came with an OEM connector that fit right into the OEM harness. So I suppose we can assume that the sensor should be good. I was thinking of trying to swap this sensor with the passenger side sensor, clearing the codes and seeing if the codes follow the sensor or not. If not I know my problem lies elsewhere.

Glyn M Ruck

Yes - It's about all you can do. Swap from side to side & see if the code moves.

Bradfr

So I tried a few different tests tonight and none of which moved the code. First I cleared the code, then I just swapped both rear connectors so the driver side connector is now attached to the passenger side and vice versa. This was to rule out the possiblity of the new sensor being bad. The code came back on as a p0161. Next I cleared the code again, then swapped the actual o2 sensors as well as the wiring so now the drivers side is reading the drivers side sensor and vice versa. I started the car and the code showed back up as the same again. My conclusion is that the only problem I could be having is the actual wiring that is running down to the sensor. I am going to attempt to actually fully trace it back to the front engine compartment SAM to verify everything in there is intact.

Bradfr

I haven't had much time lately but I recently played with this a little more. I traced the wires back to the front SAM last night. I was going to disconnect the plug and run a continuity test on each wire down to the sensor plug to verify they are good. In doing so when I disconnected some of the plugs into the computer I noticed some corrosion. It looks like moisture got in there at some point possibly shorting a connection. It wasn't real bad but bad enough to be concerned and requiring the need to clean them up. After spraying with electrical contact cleaner and lightly lubing the pins and connectors to the computer I am still getting that same code. I did not run my continuity test yet but and hope my computer is not going to need replacing from due to possible shorting.

Bradfr

Had some time off recently and played around with this a bit more. I have a feeling I may have an issue with the ECU. After further reading on this site I came across the all of the threads with oil leaking down the wire harness. Sure enough my vehicle has oil leaking on the driver side o2 sensor plugs. I have since cleaned both with no luck. Even if i swap the driver and passenger side rear o2 sensor plugs the code still reads p0161. I can only force a p0141 code(passenger side post cat) when I run the car with that plug disconnected. I also watched all of the voltages on the o2 sensors with my scan tool and it looks like the driver side averages a little lower than the passenger side.(.535v driver, .65 passenger) I am not sure if that is an indication to anything or not.

Anyone know if there is a good way to test that my ECU is not shot possibly from grounding due to oil contamination? Thanks in advance.

mercedes211995

i think i am having similar issue to you, but mine is c280 w202, i replaced the 02 sensor problem when away for week and came back. i keen on knowing if you managed to resolve it? after reading your post it may be some sort of voltage regulator?

please let me know

SGTzAMG

Was this issue ever resolved? Had the same isssue, just finished replacing O2 sensor, cleared CEL, and it came back on after turning off engine and starting back up