2002 Sentra Check Engine Light

My 2002 Nissan Sentra’s check engine light keeps coming on. It came on about three weeks ago, and our mechanic replaced an oxygen sensor. Two or three days later, it came back on. He figured the first sensor was faulty, and replaced it with another. The light came on as I was driving away from the place. The mechanic replaced some of the wires. And now, a week after that, the light came on again.

Help! Any thought on what it might be or what I should do from here?

Front or rear sensor?

This scenario is not that unusual. Symptoms can be caused by multiple problems, and your mechanic might think it is best (cheapest) to make educated guesses, replacing each one by one. For best help here to post the exact CEL codes that the engine is complaining about. If you think your mechanic may be in over his/her head, maybe look for a recommendation of a shop that specializes in your particular make of car. Specific manufacturer scan tools and other testing equipment not every shop has are often necessary to get to the bottom of this kind of problem.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Thanks for responding. I took it to autozone today, and the code is P0037. Obviously, I’m far from being car-literate. Our gas mileage has stayed pretty consistent - it’s even ticked up a little bit because we’ve put a lot more highway miles on it recently. It’s an '02, but we take public-transit to and from work, so it’s got really low mileage (73k).

Do these details help at all?


Thank you for the additional details

P0337 is a code for the crankshaft position sensor

I would say this has absolutely nothing to do with the oxygen sensor replacements.

So, the first time the light came, on the code was for an oxygen sensor, correct?

What about the second time . . . did he scan codes?

Or did he just assume the same code had reoccurred?

I suggest you get this resolved quickly . . . a crank sensor problem can result in a no start situation

I think you may have misread my earlier comment. The error code is P0037, not P0337. I’m not sure if the mechanic read the codes the second time, but my guess is that he did. It seems like the P0037 code is what keeps tripping the CEL.

It means the rear O2 sensor heater is not working. Most of the time, it means the sensor must be replaced. The heater only works when the engine is cold. The O2 sensors only work when warmed up. The exhaust normally keeps the sensor hot enough to work, but in order to get the sensor working quicker to reduce emissions before the engine id fully warmed, they have a little electric heater built in.

It could be one of the wires feeding the heater has broken or the pins in the connector have lost contact, but that is kind of rare. Most of the time, the heater element has burned out. Here is more info.


Thanks for your help.

I took it to the dealer (there was an unrelated recall). They reset the code, and said that everything tested fine. It’s stayed off in the 8 miles since.