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chagburg
06-09-2004, 19:34
I have an 02 crewcab. The allison will not downshift to 4th unless I absolutely stand on the pedal. Talked to the dealer and they said this is the way the transmission is supposed to work, although they have had a lot of complaints of this nature. I have had the update to prevent busy shifting and boy it sure won't busy shift. Has anyone else had experience like this and could you get GM to do anything? So far they have been an uncaring brick wall. I know about the overdrive inhibit switch, but GM won't pay for it and I shouldn't have to.
White Truck
06-09-2004, 20:26
I have seen this caused by a Accelerator Pedal Position (APP) sensor that is skewed. There will be no codes, but typically trucks that drive the best have 100% APP on the Scan tool with about 80% actual travel. In other words, you don't have to put the pedal to the floor to get 100% like you would on a mechanical system. Replacement of the accelerator pedal assembly should take care of this, although occasionaly the pedal has to be shimmed slightly to get the desired results.
This information is valid only if other causes of this problem don't exist and you are driving in such a manner that a downshift should occur. The trans will not downshift if an engine overspeed condtion would exist. I am sure you know this, but I thought it best to mention it.
chagburg
06-24-2004, 14:51
Took truck to the dealer for the allison not downshifting and have not picked it up yet but was told by phone the truck performed like it was suppposed to. They told me you had to stand on the pedal to get it to downshift, but according to GM specs, this is the way it's supposed to work. I am supposed to pick the truck up in the morning. Any suggestions? I am sooooo disappointed in this transmission, I would rather have a 6 speed manual.
jjackson
06-28-2004, 04:22
chaburg, I think I have read here where there is a dealer test to insure your accelerator pedal is properly adjusted. You might try a search for more info.

John
White Truck
06-28-2004, 19:49
Part Throttle Detent Downshift
Place the shift selector in DRIVE.
Accelerate the vehicle to a speed just above the FOURTH to FIFTH shift point, using less than 50 percent throttle.
Quickly increase throttle angle to greater than 63 percent.
Verify the following conditions:
The TCC releases.
The transmission downshifts immediately to FOURTH range.
Give them this information, 63% is not "standing on the pedal" Tell them White Truck says so, that oughta shake 'em up! :D :D