transmission diagnosis

[3ace]

Hi,
I have a 6.2L Chevy Suburban using a L480E auto xmsn. When I get into stop and go traffic for any length of time the transmission like stays in 2nd gear. Even if I shift into all of the other gears manually it stays in 2nd gear. If I shut the engine off and restart it everything is back to normal shifting. The transmission shop that I go to tells me it's not a transmission problem but probably something to do with the computer. He said that if the computer senses something is not right it will default to 2nd gear. When I shut off the engine the computer resets itself and that's why it works normally again. Any ideas out there that might be causing this to happen? Thanks.

3ace

[Robyn]

To diagnose this with any real accuracy you will need to plug in a scan tool and see whats happening.

The speed sensor on the output shaft may have issues or ????

The tranny on that rig is controled by the transmission control module (TCM)

There is a TPS switch on the injection pump that feeds info to the system too.

You need to see what signals are being fed to the computer.

Have you seen an SES light come on???

Any time there is a failure or "anomaly" the computer should log it.

Get a scan and see if this turns up anything, if not you will need to do a "real time" scan and see whats happening when the thing stays in second gear.

The fact that it will reset with just a KO-KO cycle suggests that it may be a sensor thats having a hicup or possibly the TCM.

Get the scans done and see what shakes out.

Missy

[JohnC]

A faulty ignition switch is a common cause of this type of behavior, too, but the first thing to do is get the codes. I think you can get the TCM to dump the codes with a paperclip. Search on ODB2 and paper clip...

[3ace]

Used paper clip trick and got a code of 12 which I believe means system is normal. I did replace the speed sensor about 2 months ago. I suppose I could have gotten a lemon. One day when I have the time I'll try to duplicate the stuck in 2nd gear scenario close to my transmission shop so that I can take it there while it's doing the problem and they can do a real time scan check. Wish me luck on that one!! :)
Thanks for your replies.

3ace