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CEL P0302 after maintenance


bglz42

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

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…

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?

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First, it would be helpful to always include the actual codes you are getting for the O2 sensors, as well as the type of device (global OBD II or Porsche specific system) used to read them.

As noted above, P0302 is the code for a #2 cylinder misfire. Any time you do some work and get a code, the first place to look is where you just were working. You may have disturbed a wire connector or pull one loose. Changing the O2 sensors should not cause a misfire.

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Thanks for your replies!

I don't know when the plugs/coils were last changed. I bought the car just a few weeks ago. I am trying to baseline everything.

I was using a generic OBD II reader.

Sorry, the first code was P0153. Happened about 150 miles after the air filter change. Used Mann filter. Besides an oil change and the air filter change, I haven't messed with anything else. Until the O2 sensors. Any idea why one would be reddish?

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Did the car come with records? I would not use a generic ODB II reader on these cars, FYI. They are known to give the wrong codes and exhibit other strange behaviors when doing so. Not saying it's wrong about this specific code but I would not want to have to rely on one. Having a good and accurate tool like the Durametric which you can depend on makes working on these cars a lot easier.

Good to post those codes as JFP said. The P0153 indicated an aging of precat (cyls 4-6). As JFP said, these shouldn't be related but they also aren't even on the same bank which I would think makes them even less related. I would agree with JFP that usually when you've just done something and then get a code, I always go back to what I was working on.

Standard Mann filters are good. This should have nothing to do with an air filter change. If you want to baseline everything, I would start by doing a code scan (and all subsequent scans) with a Porsche specific tool only.

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Thanks guys!! I will order a Durametric today.

The car came with records, but not as good as I would have kept them. Some gaps. But the car was so perfect, and maintained by a local (Porsche of North Houston) dealership that I could not pass it up.

I agree with this statement also, " I would agree with JFP that usually when you've just done something and then get a code, I always go back to what I was working on.". I doublechecked the sensor installation, torqued correctly and unplugged/plugged. Everything looked good.

I think I will start at the beginning...

First the Durametric...

Check air filter

Check connections at MAF

Check coil connections

Check O2 sensor connections

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I think you have the right plan. Even if you decide to sell that Durametric later you will be able to recoup most of your investment, so it's a fantastic tool in a lot of ways.

It's always interesting when you get a previously owned car, even with full records, and you don't have a lot of miles logged on it yourself. Gives me a new appreciation for what it must be like to be a mechanic -- when people walk in the door with a problem and you can't take anything for granted.

If everything checks from the work you did and nothing was loose, etc then you may want to clear the code and see if it returns. If it continues to return I would address the problem ASAP as not doing so could potentially damage your TWC. If you didn't pull something loose the vehicle might need new plugs and coil packs -- not the end of the world.

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Thanks Silver_TT! I have the Durametric on order, should be here by the weekend... I appreciate all the help!

I am planning on changing the coils/plugs. Curious to see what the Durametric shows...

This is not my first Porsche, but it is the oldest I've owned...(Fit my retirement plans, LOL!) A fun adventure so far!

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Durametric may very well show the same code as your generic OBD II reader -- however, this will give you peace of mind that you are reading the correct codes now and in the future, again, as generic readers are widely known to sometimes give "phantom codes" or otherwise incorrect codes. Because of this potential to give inaccurate results and lead you down the path of spending money on parts and labor that weren't necessary, I find generic readers to have little to no value when used with these vehicles in most cases.

I would hold off on the plugs/coils until you get the Durametric... and I would try to clear the code once to make sure it returns. If at that point it does in fact return, then it would be prudent to go ahead with the plugs/coils if everything else checked out ok. I just want to be meticulous to ensure that you don't potentially spend money that wasn't necessary.

Congrats on the new car!

Edited by Silver_TT
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Silver_TT, thanks for all your help! The Durametric is on the way, but has not yet arrived. I have not pulled the #2 coil to inspect.

Another data point: I had to move the car to another spot in the barn, so started it. Was low on fuel, so decided that (if CEL stays off) to go buy fresh fuel. Trying to eliminate all variables.

On driveway, CEL came on. Stopped and cleared. Once temp came up, no CEL. Fresh fuel, drove a ten mile loop back to the house and the car ran great! No codes showing on generic OBD II.

I have read a couple of reports of old, delaminated coils absorbing moisture. (I live on the Texas Gulf Coast, over 90% humidity). After heating up, and boiling out the moisture, the misfires cease. Could be my issue?

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Yes, if you live in that type of climate and the car had older gas in the tank it could definitely be related to your fuel as you stated. I think you are on the right track. I would continue to monitor the car, especially when your Durametric arrives to make sure you aren't getting subsequent misfires. Ten miles probably isn't enough to say for sure, but what you are describing definitely could cause misfires on one or more more cylinders. I would just continue to drive it frequently using fresh fuel and make sure those codes don't return. That would be the easiest and most simple solution to your trouble! If you are going to let the car sit for extended periods of time (~30 days or more) you might want to consider using a product such as Sta-bil, especially in the climate you live in.

Edited by Silver_TT
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My Durametric showed up early! Yay!

Hooked it up last night, and you guys were RIGHT! The generic OBD II reader showed zero codes, (after clearing the P0302 last week),

Durametric showed P0300 & P0302. Cleared everything, ran the car and checked again. No codes!

Apparently a generic reader can't completely clear the code out, but Durametric can...

Car is running geat now, BTW!

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Glad you got it sorted.

Your problems likely resulted from your gas and/or climate. Glad it was that simple. Some people follow strict maintainance schedules and I do also with stuff like oil changes.... but I don't change plugs and coil packs until I get real misfires. I usually don't do preventative maintainance unless it can damage the car (eg. water pump's impeller) -- plugs/coil packs won't hurt the car as long as you address the problem immediately after the onset of misfire codes (assuming using fresh gas, etc).

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  • 2 weeks later...
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.

__________________
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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.

__________________

When you pull the plug on the bad cylinder, take note of its color and level of carbon build up versus the other plugs, this will help give you a better idea why it is acting up.

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  • 3 months later...

The generic OBD II reader showed zero codes, (after clearing the P0302 last week),

Durametric showed P0300 & P0302. Cleared everything, ran the car and checked again. No codes!

Apparently a generic reader can't completely clear the code out, but Durametric can...

Please post exactly what brand and model number generic OBD-II scan tool you used.

Older models had many bugs in them. I had a Innova 3100, purchased circa 1999, that could not even "connect" with my 1996 Miata. In 2012 I purchased an Innova 3030 which had no problem reading the codes and monitor status of said Miata.

Unfortunately Innova "recycles" model numbers and IIUC what's being sold now as a model 3100 is different from the unit I bought a decade plus ago. So maybe also please post the YEAR in which you bought said generic reader.

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This thread is a few months old and has already been resolved.

As already stated previously, it's not advisable to use anything other than a Porsche-specific reader (eg. PIWIS, PST2, Durametric) with these vehicles. The Durametric is both an inexpensive and a very capable tool.

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