"check engine soon" puzzler??

i have a 94 transport(3.8)it runs great,but has developed a habit,every now and then upon starting up ,the check light will come on and stay on for the duration of the engine running,there doesn't seem to be any difference in the engine running with light on,but none the less it will stay on,if you turn engine off and restart there will be no check light on.this only happens say once every 20 times or so.any ideas why the light will come on with the start of the van,but if you turn engine off and restart it will not come on??? thanks bob

Reply to
robert -wanda fox
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most likely it is programmed to come on for things like changing the cam belt and stuff like that. Do you have it serviced regularly?

Reply to
Les Benn

Reply to
Shep

No cam belt on a 3.8 Transport and the only two instances I can remember where GM utilized a maintenance reminder scheme were the

1980 X cars with V-6 and 1981 Chevettes and in both cases it was a mechanical flag that popped up in the odometer.

The check engine light indicates that a fault has been detected by the Engine Control Module, no point in speculating when a trouble code related to the fault can be easily extracted.

Reply to
aarcuda69062

I had the same problem on my Silverado pick-up. One thing that can cause that to happen is a defective gas cap (or one that isn't tightened until it "clicks"). On a "cold start" the system closes one solenoid valve and opens another one, to see if it can pull a vacuum on the fuel tank system (part of the evaporative emissions control). It doesn't affect the way the engine runs at all. If the computer cannot pull a vacuum on the tank during the cold-start it will turn on the service engine soon light. It does not try to pull a vacuum during a "warm start" so the light doesn't come back on when you restart the car after it warms up. Is it possible that your wife/son/daughter/somebody just isn't tightening the gas cap when they fill it up? The service engine soon light won't come on until the next "cold start" if the gas cap is loose... so the person who filled it up might not be the one who gets the light. You could have a defective solenoid, bad vacuum sensor, or a leaking vacuum hose or fitting... but replacing the gas cap is cheap enough to try first.

"robert -wanda fox" wrote in message news:Fafpi.4394$Gs4.4035@trndny05...

Reply to
David Courtney

"easily extracted" hardly,you can't jump the top pins as in a obd 1 system to read codes,you can't use a obd 2 code reader to read codes,autozone and a few others can't extract the codes either.this has the transition ssystem in

Reply to
robert -wanda fox

The fact that you (and Autozoo and few others) are not properly equipped doesn't mean the codes can't be easily extracted.

I really-really-REALLY don't need to be told this...

Have you bothered to check e-bay to see what MT-2500s are selling for? You might score a $3000+ tool for a few hundred bucks.

Yes, take it to a shop that has the equipment, pay their nominal fee, get the codes, don't ask them what they mean or imply in any way that they should explain the system to you. You'll be welcome back next time...

also i'm pretty sure the problem lays with the gas cap that

So put a $8 gas cap on it, disconnect the battery to clear the codes and see if the MIL returns.

Reply to
aarcuda69062

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