whatsup

My SES light comes on after I drive about 100 continuous miles (highway). It has done this a couple of different times in the last couple of months. I replaced both O2's and it still does it. You can drive the car all day long in city stop and go traffic and the light never comes on. Go on a trip and after about a 100 miles the light comes on. Car runs fine when the light comes on. Turn off car and light goes away for a while then comes back on. Any ideas?

JDBlaze85

have you scanned the PCM for trouble codes? your light comes on, so there is a code stored in the pcm memory. From what you posted, I'm guessin that the EGR system has a problem. The Egr valve opens and closes mostly at steady highway speeds. BUT........before replacin any more parts, you HAVE to get the codes out of your car. It will help ALOT in fixin this problem. If your car is a 95 and earlier model, you can pull the codes out yourself by jumpering the "A" and "B" terminals on your DATA LINK connector. (located under the dash) By doin this with the ignition on and engine off, your SES light will start flashing. The number of flashes will give you the code. This is a cheap way of pulling a code out the car. Its great if you dont have a scanner handy. if you wanna try to pull the code out yourself, let me know and let me know how many flashes you count. I happen to have a code definition chart here and can offer better diagnostic advice.



JD

whatsup

I haven't ran codes yet...but my EGR is disconnected. It's still on the intake but vacuum hose is disconnected and plugged. Also exhaust lines to back of intake gone.

Injuneer

Just to clarify.... shorting the ALDL pins and flashing the codes on the SES light will ONLY work on 1993's. It will not work on 94 and up.

Why did you replace O2 sensors the first time the light came on?

whatsup

Someone said that might be why. I had never changed them and since I had just installed headers on it I figured might as well do it. I thought of something since my first post. I always run Ultimate 92 in it for gas...with the exception of two times. Both times SES light came on while I was traveling and running low on gas. Didn't have much choice where I could stop and get it. I always try to get highest octane # and living in Iowa that means Gasahol(gas/ethanol blend)...which is what was in the car both times SES light came on....could this do it?

Injuneer

Large quantities of alcohol in gasoline can throw the O2 sensors off. Alcohol includes oxygen, so it tends to lean things out. Run a large % with the gasoiline, and the O2 sensors will try and richen things up. If you were already on the ragged edge of setting a "lean" code on gasoline, the alcohol could throw things off.

But.... don't guess, and use the "replace-a-part" approach... that's what we condemn Mr. Goodwrench for . Flash the codes and be sure.