Car is back on the road, finally. Driving to work, check engine light comes on. After diagnosis, it's code 17, O2 sensor. Car cooled off, and I took it for a spin at lunch. Code was off when I started the car - I did not clear the code by disconnecting the battery, it just went off by itself - but came back on after 10-15 minutes of "spirited" driving. Went off again just before I pulled into the parking lot. Afternoon break, I started it up again, and again no code. Came on once again on the drive home, but went out somewhere along the way (~20 minute drive, mixed highway/city). so, it appears to only come on when the car is warm, and after some relatively high RPM pulls.

Check engine light is off now, but I need it to be off long enough to pass NYS inspection. I've pulled the connector, and the contacts look clean. Wires all look to be in good shape. Is this just a sensor on the way out? I'd hate to have to get a new one, as I plan on pulling the old downpipe and installing the newer one with wideband, MSPnP, etc. But I need it to pass inspection so I can drive it while tuning.

Also, car was spitting coolant out of the very slightly overfilled overflow tank this morning. Checked the radiator cap, and it was shot. While buying a new one at the auto parts store, I started chatting with the counter guy. He claimed a bad head gasket could allow coolant into the cylinder, and the burned coolant could throw a code on the sensor. Could that explain the spitting out of coolant even when the tank wasn't more than a hair over the full line?

Suggestions?

Edit: further info. Car does not seem to have any hesitation, misfires or loss of power. Sorry if this is more of an M.net question, but I can't seem to find any information beyond "replace the sensor".

 

I had the same experience with a dying narrow band o2 sensor on a OBD1 miata. It's interment and doesn't store the code. Just replace the sensor with a generic from a parts store. They're about $15 if you buy one without the pigtail & splice it in yourself.

 

If it's pre 1996 then the CEL doesn't matter. It'll still pass NYS inspection.

 

Thanks. I was unsure as the NYS DMV really only mentions the CEL as relating to OBDII. Scheduled inspection is 3 o'clock today.

Next up, Megasquirt (round 2)!