What timing! I'll have had my truck exactly one year tomorrow and last night the Check Engine light comes on. Actually it's running fine but I am a little concerned. The only mods are the tires (shouldn't affect anything since I have the 5 speed) and a locking gas cap. An engineer freind here at work said there could be pressure problems in the gas tank since it has been in the 90's here lately.

Any body ever heard of this? If it is the problem will the light re-set if I open and close the gas cap. I don't have the truck with me right now since I drove my Mom's car to work today. I'm just wondering if I need to set up a dealer appointment for tomorrow like I was planning.

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2000 XL 4.6 5spd 2WD reg-cab long-box 3.55 LS 265/75/16 Chestnut (not 2-tone) Raven-Cap (and a '66 GTO with a '73 455, both combined cost less than a Lightning )

 

The gas tanks on all late model vehicles are operated under vacuum, and a loose cap will trigger a "Gross Vacuum Leak" error code, which will cause the light to come on. If you tighten the cap to fix the problem it will take the PCM a little while to be happy with it and trun the light off. I think it's about 3 full warm up cool down cycles.

A defective or improper cap will cause the same effect, except of course you'll have to replace the cap to get the light to go out.

Put the stock cap back on and give it a few days to see if it's your locking cap causing it. Otherwise the dealer is going to hit you for about $75 to tell you to replace the cap.

As long as it is running OK, there is most likely nothing seriously wrong.

 

Thanks Hawkeye,

I have a feeling this is the answer.

 

My pleasure, hope that's all it is.

 

you might as well reset the computer also. just unhitch the neg ground on the battery and turn your headlights on for 5 mins. then turn them off and re-attach the battery cable.
be sure an replace the stock gas first...

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2001 F-150 4X4 Supercab
XLT 139" WB style side
5.4L V8 3.55 LIMITED SLIP AXLE


MODS:

SUPERCHIP
ROLL & LOCK TONNEAU
HOLLEY SUPERCHARGER
PILLAR GAUGES
GIBSON HEADERS AND SS CATBACK

being installed as of 6/15/01
REFLEXX COBRA HOOD
STREET SCENE GRILL

 

Found out the same thing on my mustang, just make sure the cap is tight and the computer will reset before too long, or you could disconnect the negative cable on the battery for an hour.

 

Its a sensor. I had the same problem a short while ago. Cost about $70.00 and a half hour of time at the Ford Dealer. I believe it was the oxygen sensor.

 

If the gas cap is loose the check engine light will come on, once you tighten the cap it will take up to 5 drive cycles for the light to go off. If you disconnect the battery cable, leave off for at least 15 minutes, once you reconnect the cable, start the engine and let run at idle for at least 10 minutes so the pcm can "relearn" its idle strategy. It could also be anyone of about 15 sensors. The best thing you can do is have your dealer run the test on the pcm. If you are still under warranty it should not cost you anything unless the light was turned on by any mods you may have done which includes the gas cap. Good luck!