i have a 1988 chevy1/2ton p/u and my check eng light always comes on but my engine is running good?

Answer 1

The only part John had right was about the gas cap, but not on a '88...

The check engine light will only come on if the computer senses a problem with the emission control system. Lots of times the culprit winds up being the o2 sensor, but only the codes will tell you for sure.

Engine temp, oil pressure or voltage issues will not set the check engine light.

Answer 2

Some people here have sent you on a wild goose chase.
1) 1988 is too old for fuel cap issues.
2) It is also too old for AutoZone to read the codes for you. It is NOT OBD II compliant.
3) If the light comes on immediately after start0up, and stays there, there is a failure present at start-up. The PCM doesn't read the O2 sensor until it goes into CLOSED LOOP, so the O2 sensor most probably isn't the only code present.
Recommend you go here------>

http://autorepair.about.com/library/ts/obd-i/bl-dtcs-40.htm

...and scroll down below the code descriptions and follow the procedure discussed for retrieving the diagnostic trouble codes with a paperclip.
After you have the codes, you can refer to a repair manual (purchase at a parts store, book store, on-line) or at the local library in the REFERENCE section for proper diagnostic and repair procedures.
DO NOT mistake a code as directing you to replace a specific component. It is directing your attention to a failure in a circuit or system that is monitored by the PCM.
One of the things that you might look at is the timing connector. If you have tuned the engine lately and forgot to reconnect the EST wire, the "Check Engine" light will remain illuminates constantly, because the PCM is "seeing" a failure in that circuit.

Good Luck

Answer 3

That is usually either your engine thermostat causing that. It can be sticking a little. not opening all the way, or if you've had it changed recently it have a higher temperature rating than called for; for your engine.
A particularly stopped up radiator will also cause you engine to over heat enough to cause your check engine light to come on.

Being low on oil or water will also cause the check engine light to come on, but I am sure you have already checked that.

A defective oil pressure sending unit will also cause that, as will a defective water temperature sending unit. Or bad connection on them.

Some other things to look for: Water pump going bad.i.e. impeller loose on shaft.

I have also had strange as it sounds a radiator cap cause that, and I have also had a radiator hose that would collapse cause that as well.

If your engine is fuel injected check your gas cap. A loose gas cap on a fuel injected engine will cause that as well. Tighten your gas cap until you hear several racketing sounding clicks, and have your local parts house pressure check your gas cap.

Those are a few of the more common things which will cause a check engine light to come on.

Answer 4

Go to Autozone, they will run codes for free. Also, to turn light off without checking it, disconnect the battery cable for 5 minutes. If light comes back on, there is a problem somewhere.

Answer 5

Yes, it sounds like you may have an O2 sensor that's going out. They are easy to replace though. I'd say like someone else said though to go to an auto house and have them scan it to make sure. No point in wasting money if it turns out that that's not the problem.

Answer 6

it is probably the oxygen sensor there is 2 of them one or both is bad 1 located in exhaust manifold the other is somewhere in the exhaust pipe under car

Answer 7

go to autozone they will check the computer code for free and tell you what the error is.