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Service Engine Soon Warning

First, the basic information: I have a 2000 Pontiac Grand Prix GT with 109k miles. It’s been running pretty smooth, but recently the temp gauge has been running a little high also with low coolant light coming on. If you check the coolant level in the reservoir, it’s at the proper level, and the car was serviced for this problem about a year ago and the shop pretty much cleaned the sensor, which helped for a while.

Now I know the Service Engine Soon Warning is something due to emissions control system not behaving correctly. My wife filled the car Saturday at the gas station we normally use. I thought maybe she didn’t put the cap on and turn it until you hear it click a bunch of times. So Since it was down to a quarter of a tank, I topped the tank off with premium (91 octane here in CO). I read in the service manual that if the problem was cap not replaced correctly or bad gas, it would take a few tanks for this warning light to go away. Wondering if it could be something like an EGR valve or O2 sensor that was bad? I would have thought that if it was something like those, or bad spark plug or wires, the car might run rough or the gas mileage would suffer. Not the case here. The car has been running smooth with no hesitation and gas mileage is as good if not better than normal. Do parts shops have code testing equipment that might tell me what the problem is, or do the code testing equipment tend to give a general explanation?

Does the car also have a “Check engine” light? That’s the one that counts. Sometimes they add a “Service Engine Soon” light to pad the dealers service department…

If it’s an emissions problem, a code(s) will be stored in the computer which most parts stores will read for you (free) and tell you what the codes mean. Save the codes and post them back here and we can tell you more…

It might have a Check engine light, but it’s not coming on just yet. I read that if the Service Engine Soon light starts flashing, then you need to get it into the shop asap. I’ll call my local NAPA parts store and see if they can read the code. I’ve had codes read before and the code explanation can sometimes be obscure one where you have to peel away at the layers (start replacing parts) to get to the real problem.

Turn the key to “on” and see what lights are glowing and how many different lights are glowing. Start the engine and they should all go out…

Take the car to an auto parts chain store (Autozone, Advance, Pep Boys - whatever) and ask them to scan it for codes.

Write down the exact codes (format: P1234) and post them.

These are not reasons to start guessing and replacing parts. They are called “diagnostic” trouble codes (DTCs) and there are diagnostic procedures to use to avoid blind parts replacement.

OK. Went to NAPA this morning and got them to hook up their code reader. Got P1133 code, which they said was air restriction, which could mean clogged air filter, bad O2 sensors (I have one before the catalyst and one after the catalyst), or other issues with the air (and exhaust system). I decided to go with the cheapest fix, which would be the air filter. I actually took some compressed air and blew out the area before the filter as there were a couple of dried up bugs, etc. Since NAPA told me the Service Engine Soon warning light would stay on until it was cleared manually, they told me to bring it back and they would clear it. I drove home about 3 miles, and so far (knock on wood), no the Service Engine Soon warning light is still off.

I would think that if it were one of the O2 sensors, the car would be running really rough, right? I’ve had one go bad and you get bad gas mileage, hesitation, etc. Is there any other thing besides the air filter (it actually could have been my wife not putting the gas cap on correctly, too, since I didn’t clear the code until after I filled up last night AND replaced the air filter this morning) and O2 sensor that could throw this P1133 code?