Check engine light...

[Peer]

I know I should've asked this earlier -- a couple of months ago my 'check engine' light came on. Since I was kind of "occupied" at the time, I didn't do anything about it... and then, a few days later, it went away. Any suggestions what happened there, and/or if there's anything I should do about it now?

-- peer

[Frodo]

As long as it was not a flashing CEL, probably no big deal. The code may be stored (even though the CEL is gone), so you may be able to still get a read out if you can get it hooked up to a scanner (free at Auto Zone and similar places).

[Peer]

Originally Posted by Frodo

As long as it was not a flashing CEL, probably no big deal.

Thank you for quick reply. No, it wasn't flashing. Do you have any guess what it might have been?

-- peer

[jcb986]

I had one come up when I changed the plugs...didn't get the connection on tight. During a test drive, I got a little miss after a few miles and the check engine light came on. I knew the one that I was having a hard time getting snapped back into place and it did pop lose. Once I had it back on correctly the check engine light went off after several drives. The computer will automatically reset the cell after so many cycles...I believe it's 10. So your problem could have been a misfire or anything, but the problem went away and the cell was reset. Check and see if the code is still stored, this will point in the right direction.

[Peer]

Originally Posted by jcb986

I had one come up when I changed the plugs...didn't get the connection on tight. During a test drive, I got a little miss after a few miles and the check engine light came on.

Oh, by the way, I had the car smog checked (CA) after this episode, and it passed with flying colors.

-- peer

[Bladecutter]

Originally Posted by Peer

Thank you for quick reply. No, it wasn't flashing. Do you have any guess what it might have been?

-- peer

Honestly, there are hundreds of potential codes that it could have been, and quite a lot of the codes have multiple potential causes.

The only true way to know what caused your code would be to pull the code using a scan tool, or something similar.

BC.

[Frodo]

Originally Posted by jcb986

I had one come up when I changed the plugs...didn't get the connection on tight. During a test drive, I got a little miss after a few miles and the check engine light came on. I knew the one that I was having a hard time getting snapped back into place and it did pop lose. Once I had it back on correctly the check engine light went off after several drives. The computer will automatically reset the cell after so many cycles...I believe it's 10. So your problem could have been a misfire or anything, but the problem went away and the cell was reset. Check and see if the code is still stored, this will point in the right direction.

Yeah, those little guys can be hard to get snapped back on tight, can't they? I had a CEL indicating misfire, cylinder 1, so I switched the coil packs of cylinder 1 & 2 to see if the problem moved to cylinder 2. Didn't get one of them snapped back on tight...and was running on 5 cylinders briefly. That tripped a flashing CEL.

[Gougoushu]

Originally Posted by Peer

Oh, by the way, I had the car smog checked (CA) after this episode, and it passed with flying colors.

-- peer

I was going to suggest that you get your car inspected while it is not throwing codes, so then you don't have to worry about the CEL for a whole inspection period. But it sounds like you might have done that by getting the CA smog test. Here in NY the emissions test is part of the NYS inspection process. I'm guessing CA is more stringent [CA people often complain about it ].

My CEL was off for about 9 months, I kept putting off the inspection. Now I have 1 month left, and my CEL came on yesterday ... :ah:

[Daniel R]

Bladecutter is 100% correct. Get the code read and go from there.

I made that mistake when I had an intermittent CEL. I found that if I started the car from cold and drove it hard straight away there was no CEL. If I drove it gently until it warmed up, CEL would come on without fail. I took some advice (bad advice I might add) from someone who (mis)diagnosed it as a failing MAF sensor. The advice was unplug the sensor, and if the CEL goes out then it is the problem. I did this, the CEL went away (although the car was way down on power) so I assumed it was the problem. I bought a new MAF sensor, installed it, and the CEL came straight back on!

As it turned out, the problem was O2 sensors, and the CEL didn't come on whilst the MAF sensor was unplugged just because it wasn't getting an important reading. Once the O2 sensors were replaced it was like new again.

Moral of the story, get the codes read and forget guesswork. It could be a frustrating and expensive exercise otherwise.

Good luck!

[Frodo]

Originally Posted by Daniel R

Bladecutter is 100% correct. Get the code read and go from there.

I made that mistake when I had an intermittent CEL. I found that if I started the car from cold and drove it hard straight away there was no CEL. If I drove it gently until it warmed up, CEL would come on without fail. I took some advice (bad advice I might add) from someone who (mis)diagnosed it as a failing MAF sensor. The advice was unplug the sensor, and if the CEL goes out then it is the problem. I did this, the CEL went away (although the car was way down on power) so I assumed it was the problem. I bought a new MAF sensor, installed it, and the CEL came straight back on!

As it turned out, the problem was O2 sensors, and the CEL didn't come on whilst the MAF sensor was unplugged just because it wasn't getting an important reading. Once the O2 sensors were replaced it was like new again.

Moral of the story, get the codes read and forget guesswork. It could be a frustrating and expensive exercise otherwise.

Good luck!

A related question, out of curiosity. Was it just one O2 sensor you got the code for, or more than one? How many did you replace---just the one(s) throwing the code(s) or all of them? I ask, because I'm currently in a similar situation.

[Bladecutter]

Originally Posted by Frodo

A related question, out of curiosity. Was it just one O2 sensor you got the code for, or more than one? How many did you replace---just the one(s) throwing the code(s) or all of them? I ask, because I'm currently in a similar situation.

Its always better to replace them all as a set, because they get contaminated with exhaust stream during usage, and over time, they degrade in performance.

Replacing just one or two might clear the CEL, but the chances of it coming back on soon are much higher, when the computer realizes that the unchanged ones are slower to respond than the new ones.

Think of it this way:

If the Original 4 O2 sensors lasted 12 years, and 100k miles, would you rather replace all 4 at the same time, and not need to change them again until the 200k mile mark, or would you rather have to keep inspecting the CEL every 25k miles, until all 4 are replaced at 200k miles, when you might then have to replace the first one again, etc...

BC.

[Frodo]

Except mine (the post-cat ones) are cutting out at 9 years and 53K miles

But I get what you're sayin'.