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Check engine light, again

I have a 2003 Subaru Outback 3litre with about 120,000 miles. On Christmas eve, the check engine light came on. Knowing how you feel about people who ignore the check engine light, I immediately (well, almost immediately) had it checked at the local auto parts store and was told it was an oxygen sensor. I bought a sensor and my handy-dandy neighbor replaced it. Soon after, the check engine light came on again. This time I was told it was another oxygen sensor (there are 3). So I had that sensor replaced as well. This is were it gets interesting. Again, the check engine light comes on. The auto parts store could not get a code this time so we tried disconnecting the battery for awhile, but that the light was still on. I took the car to my mechanic. They also could not get a code. They “concluded” that it was the catalytic converters and recommended replacing them in the near future but it wasn’t an immediate concern. The cost is about $1,800. I wanted some time to think about wheter I wanted to put that much money into the car, especially since I am not convinced that it is a conclusive diagnosis. So after about a week of driving with the check engine light, it goes off. I go about a week with it off, then it comes back on for a few days and that is the pattern now. On for awhile, off for awhile.

Does that sound a catalytic converter problem to you? Any suggetion on how to get a conclusive diagnosis?

I was really hoping to get 180,000 - 200,000 from this car. Other than this, I’ve not had any major issues.

Thanks,

Claire

Well, do not listen to parts counter guys for a diagnosis. Oxygen sensor codes do not necesssarily mean the oxygen sensors are bad. There are many things that influence those sensors and this is where the footwork comes in.

Vacuum leak, subtle engine misfires, etc, etc. could all trigger an O2 code and I will point out that there is no code for a vacuum leak.

Clearly they know nothing about codes and what they mean. There is no code that says replace this or that sensor etc. They say that a sensor has reported something that could be a problem and they provide a code to point to why the light came on. That code (like P1234) is were you start.

If you get us the code, maybe we can aim you in the right direction.

If the CEL is on, there WILL be a code…If there is truly no code, perhaps the engine computer has a problem…

Thanks. When the light comes on, I’ll see if I can get a code.

You can buy a code reader that will allow you to read the code yourself for around $60-80 depending on whether they are on sale. It’ll come with a manual that lists the codes. And it’ll probably work on your next car as well as this one.

I can’t think why the mechanics would decide the catalytic converters were faulty. Is there more to the story? If not, I think I’d try a different mechanic next time.

In general, you should never see a check engine light without one or more stored codes, but maybe Subaru’s have some special situations. You might try looking for a Subaru specific forum on the Internet. Maybe the problem will sound familiar to people there.

Codes can be present even when the CEL is not illuminated. They’re retained in memory.

Even if the catalytic converters are going out, just drive it. The only way it’ll effect anything is if you need to get emissions soon or if the are clogged and exhaust can’t get out. If it’s running ok just drive it.