Steve-o

On my old 99 C2 the CEL light came on and the dealer told me it was the O2sensor, which I had replaced. Two weeks later, the CEL light came back on and the dealer said it was the MAF, which was fixed. Two weeks after that the CEL light came on and I was now pretty pissed. The dealer said it could be "any of a thousand things"...and was charging me around $800. a pop! I traded the car in for my current ride...with a CPO.

Be careful!

dallasboats

This happened to me and my car is heavy modded. Ordered the 4 sensors and screwed them in myself...... very easy to do on my car but then again, my exhaust is easily accessible and has no mufflers.

pat056

02 sensor shouldn't go bad at 40,000 miles. I'd do some more checking before I replaced the 02 sesnors. Like mentioned, go to Autozone and get the code read, then clear it. If it comes on again, get it read again to make sure it's the same fault code.
My experience with 02 sensors (minimal) says they sould last at least 100k miles.

C4CRNA

Get a code reader they are CHEAP and avoid the hassel. My O2 sensor throws a CEL every few months and I reset it and I'm off. Dealer is 100 miles away, code reader in trunk and ready to go.

Wellardmac

I'm betting that the codes show a left and right bank O2 flow error. (I'll look up the codes later) and that will be indicative of a MAF problem.

htny

for some reason I thought the OP had ruled out MAF. If you haven't, at least inspect it, try cleaning it, and by all means buy a durametric or a code reader and reset the codes, wait for them to reappear

wyo996

I agree with all the above. An Actron code reader reset tool will cost less than your trip to the stealer. The cat code is just emissions and does not affect performance and you may still have a code after replacing sensors. If your MAF is bad you wil know it, the car will run like crap. I reset my CEL every 100 to 600 mi because of full exhaust and my SC. Will

Wellardmac

Well, if he doens't have the codes I'm not sure how he could rule out the MAF

As for the MAF making the car run like crap, that's not necessarily true. Mine ran fine when it was throwing up codes and needed replacing.

salayc

Does the dealer say that all four O2 sensors failed simultaneously? It would make me wonder unless, of course, someone peed in the gas tank...

nola911

I got my car back today and read the dang thing myself- p1123 is my code.

Wellardmac

only one code?

Wellardmac

If you were getting P1123 and P1125, then I'd say MAF, but with only one, then I'd revise my opinion.

P1123 Oxygen Sensing Adaptation Area 1 (Cylinders 1 - 3) - Lean Threshold

Probably just that one sensor on it's way out, but here's a link to a discussion over at Renntech that might help diagnose other possibilities.

http://www.renntech.org/forums/index.php?showtopic=3834

1999Porsche911

A code 1123 DOES NOT indicate a bad O2 sensor. It indictaes that bank 1 on the engine is running rich. Very often, this code will be accompanied by a code 1125 which means bank 2 is running rich. This code is only generated at idle or closed throttle. Your O2 sensor is working fine.

This code may be a fluke and resting it may solve your problems. It could also be caused by a leaky injector on bank 1. Run a can of injector cleaner through the tank. If the 1125 code finally appears, clean your MAF.

nola911

Yeah, just the one code right now. I do not believe they ever re-set it. I did so and will run it tomorrow and post results. I appreciate the great help guys

salayc

You're running rich, your O2 sensor is probably fine because it's telling you you're running rich, the engine is trying to adapt by adding air and hitting it's lean threshold. Any other symptoms? Where are you located?