Paul L

Hi All,

I have done a lot of search and already posted some questions. I think it could be more efficient to start a new thread.

I have a Nissan Sentra 2001 GXE auto. It ran extremely well and flawlessly until my daughter had a front end impact. After the body work, the car idle unevenly in the morning when cold and even stall when shift from P to R or from P to D. I took it back to the autobody shop that eventually sent my car to a mechanic (who is not my regular mechanic) to diagnosis. The mechanic's computer diagnosis a faulty O2 sensor and also found a dirty MAF. He did NOT replace the sensor but clean the MAF sensor. This cost me about CAD 250 already. Note that the SES never on yet. After I took the car back, the car regain the power but the cold start idling problem still exists. After I ran for about 100Kilometer on highway, the SES came on. This was the first time the SES light ever came on in my car.

I took it back to the mechanic, he diagnosis again and got the code P0171 lean oxygen and again a faulty O2 sensor. He never told me which sensor code is faulty. We replaced the sensor this time and costed me about CAD$200. After I took the car, it only took me 15 kilometer and I got the SES light on again. I am really upset.

I started doing more search and read a thread here saying that the code does not tell you what is wrong. They only tell what is being affected by what is wrong. That said if some other problem sent the wrong signal to the O2 Sensor, the O2 sensor will be wrong and I think we may have beaten the wrong horse. It may not be the O2 sensor problem.

Now, I recall the similarity of both incidents that both were happening on highway when I rev up the car to do kickdown acceleration. Do you think that means something else than the O2 sensor? What is so special when reving up the engine compare to city driving? That may be the clue.

I will appreciate if you can shed me some light so that I can talk with the mechanic again and not spending money on the wrong stuff.

Thanks in advance.

Paul

PS. I tried the cold start this morning and apparent it started well so the uneven idling may be really caused by the O2 sensors. Now we have to find out what casue the SES light come on when doing kickdown acceleration.