chingon88cam

ONLY when driving on the freeway and it's only happend 3 times in a 3 month span. what could it be? i thought about the catalytic converter, or O2 sensor. The car idles and runs great, no problems at all. The light just comes on for about 1 minute then it just goes away. I've tried getting a code off of it but nothing, any ideas? anyone ever had this problem?

92HeritageT~Top

Mine did that for a while but it was because I had removed the EGR valve for a while. I think every once in a while at about 55 mph when you're cruising and creating a steady vaccum the engine does a diagnostic to make sure it's getting the correct readings from the egr valve, etc. If not then it brings the SES light to life and sets a trouble code...

...but if you're not getting any codes whenever this happens I'm not sure.
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There aren't any changes in your engine whenever the light comes on at all?

chingon88cam

Nothing at all, engine sounds fine, no rpm changes... i just don't know. i don't have a scanner, all i do is that paper clip trick, i just don't think i can do that while i'm cruisin at 55+... (bay area drivers are as rude as they get).

Toehead

it is most likely the EGR. The EGR is only used at higher-speed cruising, so you would only get a light on the highway or on a long straightaway.

Air_Adam

Thats typically EGR related. EGR isn't used at idle, because it will make an engine idle rough, if at all. Once you get the rpm up a little bit it starts working, and the higher the rpm (part throttle) the 'more' you get... WOT I don't think it functions either, which is why I say part throttle.

Anyway, its almost surely EGR related code, as its working the most right around highway speeds/rpms. Usually its because of a failed EGR valve thats stuck open/closed, but you'll want to have it checked to see whats going on.

Toehead

it could also be a faulty EGR sensor. Some of the systems have an ECm operated solenoid that trips the EGR, as well as a vacuum gauge that shows that vacuum is being applied to the switch. If he applies voltage across the EGR solenoid and the engine stalls at idle, it is the pressure sensor.