Ok, this problem came and went and now its back. I have a 1995 Jimmy 4.3 4x4 and whats happening is the check engine light will come on and the truck will only have second and third gear. My mechanic thought that it was possibly the ignition switch because he couldn't read any codes with his scanner because according to the truck its not throwing any codes even though the check engine light is on. I'm starting to suspect that maybe the computer is the culprit, the trannies are electronically controlled on these trucks correct? Anyways im wondering if anyone else has had a similar problem and am looking for some input. Thanks guys.

 

Anyone?

 

You might wanna take it to the dealer for diagnosis. Even if you don't get them to fix it, it might cost you less in the long run. The cost of diagnosis should be reasonable.
Just tell them that you don't want it taken apart, just scanned.

 

The problem is when I get it scanned its saying that there are no codes, but my check engine light is on. This problem is driving me insane, even if I reset the computer by disconnecting the battery the engine light comes back on within 5 seconds of startup.

 

Who's doing the scan, the small garage guy or the dealer. If it's just a small shop they may not have the "correct" equiptment. The scanners the dealer use are about $6,000 and they are updated on the internet.

 

Hey i had the exact same problem. Mine would pop up a code every once in a while and the main code was P0740, which is a tranny code but is caused by electrical problems. It was weird my truck would try to take off in 3rd unless i manually shifted it to 2nd first. But all i had was 2nd and 3rd the overdrive wouldn't work on the highway. It actually ended up and being a bad ignition switch so whoever told you that might be right. Does your ignition ever not turn all the way back or can you sometimes start it without the key?

 

Chevy lover: its not a dealer thats scanning it but a friend of mine that owns a shop and has scanned my codes before and pulled them. He uses a very nice Mac mentor scan tool.

Scan tool

MrSpeedy: Mines doing the same thing yours was and I have replaced the ignition switch and the problem still persists.

 

Well I played around today a bit more and double checked the wiring on the new ignition switch, and also jacked up the truck and checked the wiring/connectors on the drivers side of the transmission and everything looks good. I'm really lost here, my neighbour has that autotap program and I'm gonna get him to hook his laptop up to my truck tomorrow and see if its throwing any codes on his autotap.

 

What I think that ChevyLover was trying say is that the scanner the dealer uses is designed to work with our computers and they have all the scans for the Body computer and the Engine Management computer so the dealer would have easier access to all the computer codes. Unless your friend paid extra for those extended functions.

But also some codes will not set off the MIL (SES). But will hang out in memory until the condition is fixed.

 

Well we replaced the transmission range sensor on the side of the tranny yesterday because in the diagnostics of the scanner it was showing that no matter what gear you put the tranny in it would show second and that didn't fix the problem. It's gotta be a short or something somewhere its just brutal to try and pin this down.