Hi,

Sorry for the non-Chevelle question, but hopefully there is a Chevy expert in the house that can help me with a problem I'm having with my tow rig.

I have a 1996 Chevy Suburban. It's a 3/4 ton 2wd with a 7.4L and 4L80E transmission. When I drive it at freeway speeds, after about 30 minutes of driving, and usually with a light load, like pulling a slight grade (not towing), it will pop out of overdrive and will not shift back into OD. I have to slow down to 65 mph to keep the revs down and look for a place to pull over. I shut the engine off and wait 2-3 minutes, then restart and everything is back to normal. When the problem is occuring, like before I can find a place to pull off, the 1-2 and 2-3 shift is really harsh.

I have had the tranny replaced (by Chevy) under warrantee for other issues, and this problem was there before the new tranny and still there after. It is not mechanical related to the tranny. It is something electrical that gets reset by shutting the ignition down and restarting.

I don't think a transmission shop would have much luck reproducing the problem so I've been living with it. However, my wife is afraid to drive it and I need to get this resolved somehow. Any suggestions???

Thanks!!!

The first thing I would do is have the vehicle scanned. You are looking for historical codes.. Find out what the codes are, and at what speed, and in what gear they appeared.

Let us know what, if any, codes are stored.

dh,
Sounds like it is going into "limp home" mode for some reason. Like GO said, get it to a good trans shop with a scanner as soon as possible after it happens so that they can see if there are any codes stored.

Will do. I'll be back with more info after scanning...

Thanks!!

replace both shift solenoids. They are different from each other.

The reason I say both is ... because you are there and the solenoids are cheap. One quit , when will the other quit?


solenoid "B" is not holding pressure for the tranny to stay in OD.

A common thing with the 4L80E