2001 GTP Transmission Problem

I have a 2001 GTP with 149,500 miles. The other day the transmission started shifting extremely hard in every gear once the car got up to temperature. It seems that the speedometer is ok under load but when you let off the throttle, it and the hud bounces. Took it to AAMCO and they wanted to install a reman. They stated that is had DTC P0730 "Improper Gear Ratio" and P0300 "Random Misfire". Does anybody have any insight about what may be the problem?

Welcome to AF.

Taking it to AAMCO was probably a mistake since they will always try to convince you to get a rebuild. When was the last tranny service. ATF and screen filter? The hard shifting may be the sign of a flaky PCS solenoid but since you have other issues......

Is this the original transmission? The only time I've seen the improper gear ratio DTC is when a 4T65E-HD was installed from another similar GM car. All that is required is a reflash of the PCM module by a GM dealer with the proper firmware program.

The random misfire DTC is an engine related issue not tranny. It can be caused by plugs, wires, coil pack, etc. Also, a CAT convertor going bad. The 2001-2002 Grand Prixs were delivered with known bad CATs. There is a Notice from GM about it posted at our Tips & Maintenance forum.

See link below.

http://www.automotiveforums.com/vbulletin/showthread.php?t=681283

This is the original transmission but it was rebuilt by Ohio Transmission at 114600 miles. The cause of the problem then was a bearing came apart and went through the planetaries. They put a shift correction kit in to improve the 3-4 shift, which they said was a factory flaw with this trans. I looked at my bill and did not see that the solenoids were replaced at that time. That was the last transmission service approx. two years ago. In regards to the flashing of the PCM, what would cause the transmission to work correctly for two years and then start acting up? I was adiment about rebuilding my transmission last time because I did not want someone elses problem.

AAMCO also was concerned with -200 adapt pressure and they said the torque converter was not locking in overdrive.

The P0730 is an uncommon DTC but can trigger for many reasons but it is a Type D DTC and does not trigger the SES/CEL light so maybe it has been there since the last tranny service which was major from what I can see. Having a GM dealer clear the TAPs (Adaptive Shift) info stored in the PCM module may resolve that issue. However, this DTC will cause maximum line pressure to be commanded and will cause the hard shifting so it may look like a bad PCS solenoid. This includes possibly inhibiting TCC lock/unlock functions. Also, corrective action could be having the dealer reflash the PCM module with the latest firmware updates.

However,....... note that since you have the P0300 random misfire DTC it best to resolve that issue first then go on to the tranny issue. That is what is setting off the SES/CEL light, if on.

There is not a CE/SES light on. I did drive it at wot and noticed a miss. At 100k I put MSD coils and wires as well as new delco plugs.

AAMCO said that they cleared the P0730 and it tripped again under normal driving conditions

How does the speedometer/hud fit in? The speedometer/hud bounces around while coasting at about 50 mph.

Check the electrical connector to the vehicle speed sensor (VSS) and VSS output since speedo data to the analog gauge and hud digital display is from the VSS via the PCM module.

Also, clear the DTCs with an odb-ii scanner and see if they come back to make sure they are not flukes.

I changed the VSS last night and had the dealership flash the PCM today. I still have the problem. The speedometer/hud issue seems to be degrading. It is registering less and less.

Now what????