Well it's not the oil level (check engine light question)

February 19, 2011 10:07 AM

First my check engine light went on. After checking the oil I saw it was getting low, refilled it. I took it to jiffy lube cause it was time for all that. Then, a few days later, the light came on again. I'm going to take it to a repair shop, but I want to know what to expect.

Just to let you guys know, the car is OLD, a 1997 Geo Prizm (exactly the same as a Toyota Corrola) with about 120,000 miles on it. Also, nothing else seems wrong with it to my ears and eyes.

posted by The Devil Tesla to grab bag (16 answers total)

I learned in my last AskMe that for no cost, you can take your car (1995 on) to most major chain auto parts stores in the US (like AutoZone), and they'll plug in and tell you the error codes your car is throwing when the check engine light is on. I would do that first to get an idea of what's going on.
posted by Cat Pie Hurts at 10:11 AM on February 19, 2011 [1 favorite]

Yeah, definitely take it to a autoparts store and get the code read. The shop will probably charge you $20 to do that and it might not end up being anything worth fixing.
posted by ghharr at 10:13 AM on February 19, 2011

The check engine light normally indicates an emissions problem. A typical one is failing O2 sensors, or PCV valve. Many of the things that can cause the CEL to come on are small, cheap, simple fixes. Some are not, but if the car otherwise seems to be running fine, there's a good chance it's something small.

The amount of oil in the car has no bearing whatsoever on the CEL.
posted by tylerkaraszewski at 10:19 AM on February 19, 2011

120K scheduled service ?
posted by lobstah at 10:19 AM on February 19, 2011

I'm going to take it to a repair shop, but I want to know what to expect.


As mentioned, without the codes from the module that triggers the light coming on, there is absolutely now way to tell what it may be nor how much it may cost you. Get thee to a place that will read the codes before you book it in, and then come back to us.

In the good news department, there is an awful lot of stuff on a 14 year old car that can be completely ignored if it only goes wrong enough to trigger the light, though (ie no other symptoms). How do you stand legally? Are there applicable emissions or otherwise regular checks that an engine light would mean a fail?
posted by Brockles at 10:24 AM on February 19, 2011

Depending on where you are, you may need to have whatever it is fixed, as many areas run emission tests via computer on 1996 and newer cars. In these tests, a check engine light is an automatic fail.

One really dumb thing to check if you get a CEL - is your gas cap tight? A loose cap will trigger the light. If you want to learn more about how your car's computer triggers the light, google "OBD-II."
posted by azpenguin at 10:27 AM on February 19, 2011

I know from recent experience that Autozone will check your OBD for free - just take the car in and ask them to read the code for you. That said, make sure that your fuel cap is screwed all the way on - it's a quite common cause of the engine light coming on. Depending on which state you live in, you'll have to get whatever the problem is fixed - and, assuming that the engine is running well otherwise, it's probably an easy repair - before your next emissions test. CR has a good summary of what you should do.
posted by caminovereda at 10:28 AM on February 19, 2011

In my experience the Check Engine light going on means that the Check Engine light has gone on. In one case it was the actual engine sensor that had gone belly up and in every other case the light went off after I refilled the car with gas and made sure that the gas cap was tight.

I'm not saying it's nothing and if you can get it checked cheaply (I did not know about Autozone - that's awesome) then do it. But I'd bet good money on it being nothing of any consequence.
posted by It's Never Lurgi at 10:46 AM on February 19, 2011

I suggest buying a code reader. I got mine for $80 at an auto store. This way you will atleast know why the code came on.
posted by majortom1981 at 10:47 AM on February 19, 2011 [1 favorite]

I suggest buying a code reader. I got mine for $80 at an auto store. This way you will atleast know why the code came on.

And I got one on sale for $30! Seriously, it's a great investment.
posted by InsanePenguin at 10:53 AM on February 19, 2011

Could be any number of reasons but you'd do well to start with finding out what the engine computer thinks has gone wrong. As others have suggested you'd use a code reader to extract this info.

As to your oil situation, how low had it gotten? And how regularly have you been changing the oil? It could have been your oil sensor detecting a problem. Like the oil pressure was too low, or the oil temp had gotten too high. Or it could be the oil sensor itself has gone bad. The latter is more likely if the oil wasn't changed on a very regular basis. Oil that's neglected can gunk up. This can cause a sensor to get gummed up and fail. It can also cause other more significant engine damage (the gunk can clog a crankshaft bearing and cause considerable damage to it).

Get the code read ASAP. That will help tell you where to start.
posted by wkearney99 at 11:26 AM on February 19, 2011

If your home state is anything like New York, you can't pass the annual inspection with the Check Engine light on. So even if the issue is something you can hold off repairing, it may not be possible to wait forever. But it's not like you didn't get your money's worth out of your Prizm.
posted by tommasz at 11:39 AM on February 19, 2011

And if your home state is California you are not going to be able to take it to an auto parts store and have it read for free or borrow a code reader. There was a lawsuit awhile back where someone was claiming that letting people use them was "operating a repair business." You can get a basic one very cheaply that can literally pay for itself on the first usage.
posted by Big_B at 1:38 PM on February 19, 2011

2nd'ing the O2 sensor. If the car still sounds like it's running fine but the light is still on, it's probably the 02 sensor or something having to do with emissions. It's fine to run on for a little bit, but will damage your engine if you don't get it fixed.
posted by Polgara at 4:12 PM on February 19, 2011

I know I'm a little late to the game here, but here's my two cents...

sometimes transient things can trigger a CEL, as mentioned above, a loose gas cap. I would suggest disconnecting your battery completely for at least 10 minutes. this should completely clear any codes currently in your ECU. reconnect your battery and go about your way, after making sure that your gas cap, oil cap, etc are all tight. if your CEL comes back on, take a note of when, where and what conditions, type of driving you have been doing. doing these simple things will help you gather more data if you do take it to a shop/parts store. sharing the steps you have taken will at least show some guys at the shop that you're not a rube, and will help them rule some things out if the OBD-II code they pull up with their reader is fairly vague.
posted by Bohemia Mountain at 8:00 PM on February 19, 2011

It ended up being a failed O2 sensor, the dealer fixed it for a reasonable price and I'm driving without the light on now. But yea, next time I'll hit the auto parts store and get it checked out ahead of time.
posted by The Devil Tesla at 2:27 PM on February 22, 2011