I've got a posting on the Bonneville website on this topic, but I've always had good luck with assistance on this site for my other vehicle, so I thought I'd give this topic a shot here....

I've got an interesting problem with my 2001 Buick LeSabre. It's got the base L36 V6 plus 4T65E transmission, with 89,000 miles on the powertrain. I bought this car about two months ago, and I noticed that when I depressed the accelerator about 1/2 way at 75 MPH it appeared that the transmission shifted down too many gears, as the revs were way too high for what I would expect to be a 3rd gear downshift at that speed. ALso, I noticed that in town, it appeared to shift too late from second to third gear (revs too high).

I took the vehicle into the dealer for a look, and they said that the transmission is not shifting into third gear AT ALL (upshift or downshift). It was going directly from 2-4 and vice versa. The dealer's solution was a brand new transmission (of course) at $2900!

I've got a vehicle scan tool software package on my laptop [car code OBD-II], so I connected and went for a drive, below are the results:

* When I place the shifter in D2, and manually upshift to D3 nothing happens.

* Looking at the transmission status information there are no faults or problems (detected) with any of the shift solenoids, TCC solenoids, shift pressures, etc...

* The vehicle computer appears to be attempting to command the transmission to go to the correct gear: When I manually move the gear selector from D2 to D3, the proper solenoids appear to activate to cause the transmission to shift from 2 to 3. The same holds true for D4 to D3 manual commands.

* The feedback of what gear the transmission is currently in (manual commands or in Automatic) appears to be the correct one selected (meaning the feedback indicates that D3 is engaged when it should be, but it is really in D2).

* There are no fault codes or anything unusual that can be picked up using the standard OBD-II GM interface.

It appears that whatever the mechanism that causes the transmission to shift, and the feedback of what gear the transmission is really in appears to work. But the actual shifting does not take place.

Has anybody experienced anything like this? Is it true that it's rebuild time? What are my options, or things I can check before taking the plunge for a new tranny?

All thoughts are appreciated!

 

For the first half of the thread it about gave it away. Sounds like a TV cable adjustment (throttle valve cable). It is connected to the throttle, near the throttle cable. But seeing as this is a newer vehicle, the trans prolly gets the throttle signal from the TPS, thru the ECM, or PCM. Hence the 4T65EThere will most likley be a solenoid that actuates the throttle valve in the valve body of the trans.

That valve denotes how much pressure is applied to hold the gears open longer. Depending on engine load. Load is determined by vehicle speed, engine RPM and thottle position. If you go to full throttle, let's say, it would kick down a gear or to a gear that would give you more pickup. Depending on the vehicle speed and the engine RPM, it might even kick down two gears. THat's what's called 'ultimate downshift'.

I'm not an expert on auto's, but I did go to school for Auto Tech. -So I know enough to be dangerous.

Hope that helps. Sensor or something.... I could be wrong to.... Feel free to tell me to FK off if need be...