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Too much oil - can cause check engine light?

(2002 subaru impreza wrx, 2.0L turbo)

Recently my check engine light came on, and has stayed on steadily. I noticed that the engine oil is a bit high on the dipstick. My engine has always burned oil (maybe a quart every 2-3k miles) and I usually do add a quart when I see it getting low, between proper oil changes.

I’ve read about the basics of how too much oil can damage the engine (crankshaft causes oil to froth up, decreases oil pressure, etc), so let me ask some specific questions:

- just how much oil would be too much? I think I may have put as much as a quart too much.

- what are the symptoms of too much oil? I have driven the car several hundred miles since I last added a quart. There are no performance or behavior problems that I have noticed, except for the check engine light. So can they be related?

The car has 150K miles on it, so normally the check engine light wouldn’t surprise me at all. But I am concerned about the high dipstick level and whether I may have caused it.

Thanks in advance.

Go get the code(s) read at autozone. That will point you in the right direction.

Get the codes read to see which of the thousands of possible issues is being reported. One of the things that can’t and won’t turn the check engine light on is the oil level.

I wouldn’t put more than a half quart over full in.

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.

Heh, it was a P0031 - apprently something to do with the heater for one of the O2 sensors. That seems fairly unrelated to motor oil, to put it mildly.

Thanks for the replies. I’d still be interested in any thoughts on the symptoms of too much motor oil. Or what to do, if anything, about the P0031, which seems pretty minor.

If you check your oil and it doesn’t look like its foamy/full of bubbles then you likely have no problem. Its also simple, though, to just keep the oil within the marks on the dipstick.

Here is some info on P0031:

I wouldn’t ignore it, nor would I assume that the sensor is bad since the problem could be in the wiring for the sensor. Either way, it won’t be all that easy to deal with and a good shop should be able to check out the circuit for that sensor & the sensor itself.

Thanks. Would it be realistic to expect the shop to fix just the heater problem on the sensor or will they insist on just replacing the entire sensor? I bet the latter.

The heater is part of the sensor - so if the wiring to & from the sensor is intact & healthy then the sensor gets replaced.

Oh, I get it. That also means that replacing the sensor won’t even necessarily solve this problem. Ok, thanks.

One more argument for my idea of a car that talks to the owner, and tells whem in simple english (bi or tri lingual for spanish or other?) just what the problem is, and how urgent it is, and also when it needs is schedualed service.

The problem is that it would be just about impossible for the on-board diagnostics to narrow it down to the defective component. It only knows what inputs that it has are not right, it doesn’t know why. You could add a lot more sensors and wiring to help it to better diagnose the issues, but then you are just adding more stuff that could fail. You’d then have to add more stuff to diagnose the stuff that you added to diagnose the original sensors. It’s a no-win situation.