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2000 GMC Sierra, engine light came on today

Driving from work today the engine light came on, it is 2000 GMC Sierra, out of warranty with almost 50 000 km. I got my OBD-2 software going, read one code, P0442 Evaporative emission control system, small leak detected. I was bit puzzled where to look for a problem, opened and retighten my gas cap, just to convince myself that it was tight. Opened the hood looked around, not much to see, I was looking for broken hose or something. Cleared the code, run the truck for a while no trouble code set again. Will try it tomorrow on the way to work, at highway speed. I think the engine light was set today at highway speed, at least when I notices, if that makes any difference. Anyone would have any experience on that and could give me a hint or two? Thanks in advance,

Ziggie

Reply to
Ziggie
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Replace your gas cap.

Doc

Reply to
"Doc"

The followup

No codes set today

As the mather of fact I got locking gas cap shortly after I bought it, 3 and half years no problem. I still have original one, so if problem comes back I will use that one

Ziggie

Reply to
Ziggie

Just wondering how the cap helps emissions and/or why the ECM should care? I would think if anything that should be an idiot light "ya forgot it moron!"

~KJ~

Reply to
KJ

Fuel vapors are harmful to the atmorphere, hence the EVAP system traps vapors from the fuel tank and stores them in the charcoal cannaister located underhood until the motor fires and creates vacuum to the cannister and/or the solenoid kicks open (if equipped). A leak in this system is an EPA no-no, hence the SES light and the "small leak detected" message. Same reason we now have POST catalytic 02 sensors.

Doc

Reply to
"Doc"

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