I have a 2002 Subaru Impreza RS. My check engine light lit up with the code p0136 which points to a rear oxygen sensor circuit malfunction. I had the rear oxygen sensor replaced with a original Subaru part, but the check engine light comes back with the same code. The work was done a week ago and I've cleared the code with my ScanGauge several times, but it keeps coming back. If it's not the part itself, what could it be?

 

Also, I don't know if this could possibly be related, but the light started a day or two after I had work done at the dealer. They replaced the head gaskets and the right rear wheel bearing. I went somewhere else for the oxygen sensor replacement because I thought it would be a simple job and that I didn't need to spend the extra money at the dealer.

 

Any suggestions as what to do next? Thank you.

 

Doug

Welcome to the forum. As you noted, the P0136 code refers to an O2 sensor circuit problem. Therefore, besides the sensor, the wiring could be the culprit. Based on what you said, it's possible that the wiring was damaged or a connection was disturbed during the work done by the dealer.

It can be caused by mixture problems, air leaks into the exhaust, contaminated cat.

 

You should take it back to the dealer and explain that the problem wasn't there before they worked on the car.

The voltage output from the rear O2 sensor can easily be monitored by the dealer with a Select Monitor, or someone else can look at the real-time data with an OBD-II scan tool. That voltage, and whether it's steady or varying (and to what degree) can make determining where to next look a lot more obvious.

COuld be an exhaust manifold leak, can also be the front sensor. The easiest thing to do is check the electrical connections at the sensors to make sure they are tight. Unplug them then plug them back in. Make sure nothing is broken.

 

 

I lost a rear o2 sensor to road debree, so it happens.

 

 

nipper

You need to check the wiring between the ECU and the O2 sensor for a problem. One common problem for this kind of thing is the wiring can touch the exhaust system and damage the wiring. Bad connection at a connector is another source of trouble.

Since it only started happening after the other work I would take it back and give them the option to fix it, then if it turns out to be something serious that they have done they can't blame you for either ignoring the symptom or "messing around" with their work. I'm a self employed mechanic and I always want to hear if there is any hiccups after I've worked on cars, for my sake and the customers.

I apologize for taking so long to update this thread.

 

I took it back to the dealership that did the original work and asked them to look at it. They found a pinched wire in the harness to the oxygen sensor. They repaired it, and I was not charged. The check engine light has not come back since then.

 

Thank you all for your help.

 

Doug

Thanks for the update Doug. That is a pretty common problem.