CEL after maintenance
 

Bought a very clean, one-owner and well-maintained ’01 Boxster S with 38k miles. Ran great!

Changed the air filter after about 500 miles. Popped the first CEL . Code read aging O2 sensor bank 2. Cleared, ran fine. Would display CEL on occasion and, while I waited on the parts to arrive, I would just clear them out with my OBD II tool.

Changed the sensors on Sunday. Started, and immediately began running rough and blinking CEL came on. Read code, P0302. Bad coil possibly? After changing the O2 sensors?

Thinking of possible causes: all the way back to replacing the air filter. Could I have installed it incorrectly, maybe rolled the gasket and air is getting in? It looks fine, but I might buy another and try again. After I change that coil out, of course…

Might order a Durametric and dig a little deeper...

Another data point: the left side upstream O2 sensor tip was completely white in color. The right tip was dark reddish... don't know if that means anything but it stood out to me...

Any ideas?

I had a CEL indicate the Catalytic converter was not up to spec.

Cleared it 4 months ago and it never came back.

I would check the sensors cabling for loose or dirty connections first before
starting to replace things.

When you changed your air filter, did you disconnector or clean your MAF sensor? Go back and double check the MAF connector. Might want to clean the sensor as well.

No I did not check the MAF. I will now though... Thanks!

I noticed in your original post that you had a blinking CEL. A blinking CEL indicates a serious problem which calls for shutting down the engine before substantial damage occurs.

Perhaps a few of the more technically savvy folks on the forum could suggest what to do next. If it were me, I would tow the car to the repair shop and let them diagnose the problem because don't like to take big risks.

A durametric cable is really valuable if you are going to maintain the car yourself over the next several years

Had to start the car to move it into my barn yesterday. Checked for code first, nothing. Started and ran fine.

I think I will start from the beginning...

Check air filter
Check MAF connection
Check all connections at coils and O2 sensors.


Thanks for all your replies!!

Jim

Your car is almost like mine, 2001 with 38k on it. I had to replace my MAF sensor, it went bad and it fixed my CEL for a lean engine fault. Since you changed your O2 sensor, try getting a new MAF and reset the ECU. She should run just fine after that.

The thing to remember here is that the CEL codes are not always 100% accurate, any good mechanic will tell you. It nearly points you towards the area that could cause the fault but it could be upstream or downstream so first change the least amount in parts with the biggest influence in engine performance = MAF sensor.


Best

Thanks Soucorp! I just ordered a Durametric. I think my OBD II reader was a little too generic...

Durametric should arrive via UPS tomorrow... but in the meantime...

I put some fresh fuel in and ran it all weekend. No problems at all, ran like a champ! That might have been the problem all along... I bought fuel on the way home from Boxstoberfest, (not at my go-to station), and the fuel might not have been good...

LOL! Spoke too soon...

P0302 code is back. I bought a coil, and will replace the number 2... will report back after.

You need to post what a 302 error code means, or if you don't know, ask for what it means.

p0302 is a cylinder 2 misfire

Still chasing that misfire! Must be the plug...

I swapped the coil out for a new one last night, (just had a few spare minutes to work on the car...)

Still misfiring on cyl 2. I checked all the rest of the cylinders, and they were fine. Just cylinder 2..

I intentionally did not pull the spark plug, becasue I am trying a systematic approach to eliminating the real problem. Tonight I will pull the plug and replace. When I isolate the problem, I will replace all of the coils and plugs.