The other day our CEL came on; no symptoms, otherwise. It went out for a bit, then came on again, and then went out.

I borrowed a friend's code reader today, and there were no codes showing when I checked the truck this evening.

Then I drove the truck, and the CEL came on again! So, when I got home I used the reader thinking, now I'll get the code(s)! But there were none! I tried the reader with just the key in the on position, as well as with starting the truck, with no luck.

What could cause the CEL to come on without affecting performance and triggering codes?

 

"Parts Store" readers can't pull all the codes.
A Dealer-style reader is sometimes needed.

Example:
I had auto tranny problems.
CEL on, Autozone reader showed zero codes.
Dealer hooked up their tester/reader, found 3 tranny related codes.

 

Can you find someone with a Smarty and try to pull codes with that? I'd bend over backwards trying to find alternatives to a dealer.

 

From the FSM it looks like the MIL (check engine light) can be pretty complicated. It can be emissions related or something with the PCM, ECM, or CCD bus. There are about 100 codes that can set the MIL. The MIL may or may not go out after a certain number of "good trips" and may be set when the light is actually off. The only way to erase any MIL is to use a DRBIII scan tool to check and clear them. The FSM also mentions disconnecting the battery to erase codes, but nothing specific. I don't know if only dealers have DRBIIIs, but a reputable garage might know....

 

Thanks, everyone. The scanner/reader used was a MacTool. I made arrangements to go to my mechanic and have him pull the code(s), $75 ouch! But at the last minute, I decided to check the oil. It was pretty low. I added oil, and voila, the light was out when I started up! I drove around all day and it never came back on. It was at the back of my head that the times when the light had come on, the truck was parked in a hilly spot. But why wouldn't the oil light come on instead of the CEL if it that low? And, now I have to figure out where the oil is going :-(

 

I believe that low oil pressure will set the MIL. It might have been intermittent enough to set the MIL but not the oil pressure light. The MIL will stay on, but the oil pressure light only comes on when the pressure is actually low, if that makes sense.... Glad you got it figured out cheaply, though....

 

This story isn't over, yet. The cel went out, but then my fuel pressure dropped to zero and I had to replace the lift pump (again...). Have fuel pressure again but the cel is back. Oil level is in the safe range. Only code I got with our new Autel Maxiscan was "module $D1" and "engine." Anyone know what those mean?

I ordered a new oil cap in hopes it is just that the seal has blown. Any other ideas?

 

Sounds expensive. I guess the "engine" just means you need to change out the engine. Case closed, heh, heh....

 

I'd find another mechanic if he wanted $75 for a scan. Mine loans me his scanner if I ask but I give him last bid on a project and send referrals. Still a few scans at that price will pay for the equipment.