Intermitant Check Engine Light

OUMike · September 3, 2006

ok...so I was headed to school a couple days back and I noticed my check engine light came on. Right before I got to school (about 15 miles) the light shut off. I spoke with my dad over the phone and we decided to call the dealer and see about taking it in.

After I called the dealer he mentioned that a loose gas cap could trigger exactly that. I walked out to my truck only to find that my gas cap was indeed loose. He told me that after I tighten it up and drive it for like 30 miles the computer should reset. So far all is good.

Except the light is still coming on. It goes off after 20 miles or so, but it does come on later on. Does anyone have any insight into this? Maybe replace the gas cap?

Thanks in advance.

redvett · September 3, 2006

Gas tank vapor test didnt start until OBD2 came on vehicles in 1996 up so thats not it. Read the codes.

OUMike · September 4, 2006

nah I dunno.

The gas cap was most definatly loose, and the light seems to be staying off for now.

Thanks anyhow.

OnyxMAX · September 4, 2006

take it to someplace that reads the codes for free, and get it cleared anyway.

OUMike · September 4, 2006

take it to someplace that reads the codes for free, and get it cleared anyway.

<{POST_SNAPBACK}>

hmm. AutoZone does I think right?

Thanks fellas.

Wingnut · September 4, 2006

AutoZone and O'Really's both do it here.

redvett · September 4, 2006

OBD1 can be read by using a paperclip and jumping terminals A & B at the ALDL plug under the drivers side of the I/P a 12 code will be a check and then the codes. Clearing codes only requires the battery terminal to be unhooked for a minute or two.

KICK · September 4, 2006

older mod's dont have the gas cap problem so that isn't it.

you have a code that is coming and going, that is why it is off and on regarding the light. if CEL stayed on for any length of time it will have stored a code.

you can jump it at the ALDL with a paper clip, that will give you the trouble code, could be anything in your case.

OUMike · September 5, 2006

older mod's dont have the gas cap problem so that isn't it.

you have a code that is coming and going, that is why it is off and on regarding the light. if CEL stayed on for any length of time it will have stored a code.

you can jump it at the ALDL with a paper clip, that will give you the trouble code, could be anything in your case.

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what is the ALDL? Where will it display the code?

Thanks again everyone.

thecraft · September 5, 2006

See these two websites, both should explain the procedure and give you a list of codes:

http://www.troublecodes.net/GM/ - Good list of codes, but the instructions are vague.

http://tvoffer.tripod.com/gmcodes.htm - Better instructions, but only a small list of codes.

KICK · September 5, 2006

older mod's dont have the gas cap problem so that isn't it.

you have a code that is coming and going, that is why it is off and on regarding the light. if CEL stayed on for any length of time it will have stored a code.

you can jump it at the ALDL with a paper clip, that will give you the trouble code, could be anything in your case.

<{POST_SNAPBACK}>

what is the ALDL? Where will it display the code?

Thanks again everyone.

<{POST_SNAPBACK}>

ALDL= assembly line data link, it is generally within 12 inches of the steering column by your knees, and in your case is a 2 row ,12 pin connector.

you jump terminals A to B with ignition on, engine off and count flasshs of CEL.

OUMike · September 13, 2006

Thanks everone for the help. Ended up being EGR Valve and Cylinder. All is good now. Let a local dealer that I trust do the work. Kinda pricey ($339), but I needed it right now for school.

I probably got hosed eh? Where is the EGR valve on this truck? 94' 4.3L.

95Sierra2500 · September 13, 2006

I was just going to suggest an O2 sensor or your EGR valve. Like as soon as I read the first post. Glad I read on to the bottom.

sjspor · September 13, 2006

Just something to remember, many times an EGR valve, and it's passeages just need to be cleaned. Note the dealer did'nt do anything wrong by replacing the valve, they just don't want you back if the cleaning did'nt solve the problem. This more of a DIY thing, garages don't make money if you keep coming back.

OUMike · September 13, 2006

Yea. It runs great now. Just kinda sore in the wallet if ya know what I mean. This dealer has always done really good work for us though. My truck was just as clean as I left them with it. Except the outside...stupid rain.