This is a 4 cylinder 5 speed car with 170K on it. The check engine light came on last month so I took it to AAP and the it was an O2 sensor code. I figured because of the mileage I replaced them both with Denso sensors. This car has also never consumed any oil between oil changes yet it was a quart low when I checked the level about the same time I replaced the sensors. I replaced the PCV valve which had some oil in it. It also seemed as though the car was missing or hesitating at times. So I also replaced the plugs and also cleaned the throttle body and mass air flow sensor as well as checked my air filter.


Just last week the check engine light came on again so off to AAP and it was the O2 sensor again. Light went out a day later. So it came on again 2 days ago and went out again.


So what else may be causing an O2 sensor code to come on besides maybe having a faulty new Denso O2 sensor? Does the catalytic converter throw its own code if it is bad? Does a throttle position sensor throw its own code? We drive this car a lot and love it so I don't want to do damage to the engine if something is going bad. Any suggestions?

 

What is the actual code? They start with the letter P and have 4 numbers, like P1234.

 

P1039 Bank 1 Sensor 2

 

The code can be caused by a bad sensor (you ruled that out), poor connections at the O2 sensor or at the PCM. Damaged wiring or less likely the PCM.

I'd unplug the sensor and check the electrical connection. Also inspect the wiring. I believe the connector and harness wiring is under the passenger seat.

 

You are correct. The connector is under the passenger seat. The tech at Advanced Auto said that it may be possible if I used a different gas that a detergent or something different in the gas may have triggered it. Any truth to that? Does a faulty gas cap throw a different code or could that be a culprit also?

 

Do you have a ULEV engine?

 

No, it is the 2.4 ITEC K24A4 engine from 2007.

 

Well, the light came back on last evening. Sure is frustrating. Connection under the seat is fine. Would a bad PCM give me that code?

 

Do you have a exhaust leak? And the code is PO139 correct?

 

No exhaust leak and the code is correct. If PCV was bad and had caused oil blowby to contaminate the catalytic converter would the downstream O2 sensor pick up on that and throw a code?