Transmission Slipping in 1st gear

[kennem7]

I own a 2000 Grand Prix GT with the 3800 V6 with 84K miles.

Recently, my car began to act a bit strange. After I drive it for a significant period of time (hour or so), 1st gear seems to be acting a bit erratic. When pulling away from a stoplight, etc, i think the transmission is slipping, but only in 1st gear. I'd probably best describe it as feeling like the "surges" you get with a worn clutch on a car with a manual transmission.

I recently had the ATF changed, and before that around 50K miles, but i don't remember if it was "flushed" or not, which I've heard can do more damage than its worth. Is my transmission on borrowed time? or is there any chance it is something else?

[BNaylor]

Welcome to AF.

Can this be described as a launch shudder? From a dead stop what does it do when you step briskly on the accelerator. Do you get the slipping in manual shift D1?

[kennem7]

I guess that might be a way to describe it. It is "more severe" the quicker I try to accelerate.

I'm not quite sure how best to describe it. If I accelerate quickly from a dead stop, its almost like the gear will engage...then disengage...then engage again. It will do that about 3 times or so before it shifts to 2nd. Its kind of a "surging" rather than a jolting. Kind of why I equate it with a worn clutch.
I hope the description helps.

2nd and higher gears act normal.

It also only happens after i've been driving for around an hour or so, so I'm not sure what to make of that either.

I havn't tried using the D1 selection. I'll try that tomorrow and post back.

[BNaylor]

Yeah that sounds like launch shudder to me. The reason why I requested that you try manual shift is to help determine whether you have a line pressure or pressure control solenoid (PCS) issue. Also, consider getting it scanned with a scanner capable of retrieving tranny DTCs.

[kennem7]

interesting...I don't notice the problem in the "D1" mode. what would that indicate?

I also had been looking into buying an ODB-II scanner. Can you recommend one that would also be able to read the transmission codes?

Thanks

[BNaylor]

Thanks for getting back with us. It indicates a possible PCS issue.

The better Actron brand obd-ii scanners can read out generic and enhanced/manufacturer specific DTCs which includes transaxle related. For example my Actron will read out a P1811 (max adapt, long shift) DTC if present. Of course there are other good scanner brands along with the PC Laptop based programs like Autotap. Note: Many tranny DTCs may not trigger the SES/CEL light.

[kennem7]

Scanned the car today, but no codes were stored...would that eliminate anything, point towards anything?

[BNaylor]

Was this with a scanner capable of retrieving GM extended tranny codes? P1XXX?

You could still have a line pressure issue which is PCS related even without the DTCs. The line pressure can be tested to see if it is in specs. Especially since the problem does not show up in manual D1. The PCS is not used to control line pressure in manual.

[kennem7]

The scanner is the AutoEnginuity PC Scantool Base Version (not the GM enhanced software) (www.autoenginuity.com/). I've not been able to figure out whether it reads the P1xxx series codes yet with the base version.

I'm pretty sure The Enhanced version will. I may upgrade for that version, which would probably help anyway.

[kennem7]

got the enhanced software....and sure enough P1811 showed up.

[BNaylor]

Checkout the link below which may be of help. Located at our Tips & Maintenance subforum.

Click here