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Steve Morris' 1967 GTO

2021 May
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Hello, this morning while delivering newspapers I shifted from park to drive facing down on a hill and heard a strange noise as well as felt like I got a tap from someone hitting the back of the car. Now it hard shifts from park - drive then shifts hard from 1st to 2nd, from reverse or neutral - drive with hard shifting from 1st to 2nd. My check engine light is not on so no codes to check. I'm out of my extended warranty so if somebody could please help with some suggestions I would greatly appreciate it. Thank you!

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Hi Becky, sorry to hear that your G6 is having problems. 

There are a number of things that it might be. First thing I want to make you aware of is a Technical Service Bulletin that GM issued on this problem. I think this problem was specifically for the G6 GTP with the 4T65-E transmission, but I think you will get the jest.

#1 Possible Cause

Bulletin No.: 06-07-30-034

Date: December 20, 2006

Service Engine Soon (SES) or Check Engine Light On, Harsh Shift, DTCs P0742 and P2761 Set or Just P2764 Set (Replace Automatic Transmission Wiring Harness)

2006-2007 Buick Allure (Canada), LaCrosse, Lucerne, Rendezvous, Terraza
2006-2007 Chevrolet Impala, Malibu SS, Malibu Maxx SS, Monte Carlo, Uplander
2006-2007 Pontiac Grand Prix, G6 GTP, Montana SV6
2006-2007 Saturn Relay

with 4T65-E Automatic Transmission (RPOs MN7, M15 or M76)


Some customers may comment on the Service Engine Soon (SES) or Check Engine light being illuminated. Upon investigation, the technician may find DTCs P0742 and P2764 together or just P2761 set as current or in history. Also, the customer may comment on a harsh shift.
The tan wire (1) of the Torque Converter Clutch (TCC) Solenoid Valve harness may be incorrectly routed around a metal retaining clip causing a chafe in the wire insulation, resulting in a short to ground. The harsh shift concern is due to the default code causing high line pressure to be commanded.


If diagnosis indicates a grounded circuit, replace the transmission wiring harness following the published replacement procedure in SI. Be sure to route the tan wire out of the metal clip.

When servicing 2007 vehicles, the metal clip for the temperature sensor connector on the new harness must be removed and discarded prior to installation. Reuse the plastic clip from the old harness.

#2 Possible Cause

I have also read that the transmission solenoid can get dirty or fail and cause the harsh shifting problem  that you've described. Its an inexpensive part but it is in a terrible location and require lots of labor.

#3 Possible Cause 

Low transmission fluid - highly unlikely, but you eliminate that quickly by checking the transmission fluid level with the dipstick. If its low, add transmission fluid per your owner's manual instructions.

#4 Possible cause

Computer problem - have the computer re-flashed. Again an unlikely scenario but it might help.

#5 Possible Cause

Internal transmission damage - requires a professional to assess and fix. It will be the most expensive option since the old transmission will have to come and either be replaced or repaired. Last resort option.


There maybe other problems that I've not thought of, but I think this covers a lot of bases.

I hope that helps you somewhat. Feel free to ask questions.


Edited by Frosty
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