slipping trans?

[davepk74]

I just recently bought a 2003 envoy xl with 45,000 miles on it.
I have had it for a week now and i notice at around 35-40 miles per hour the transmission is slipping. Is it true that the transmission has a break in period when someone new purchases the car and there driving habits are differrent, therefore the transmission is trying to learn my driving technique? I am going to make an appointment soon for it to go in to get looked at if it is not normal.

[maxwedge]

No, there may be some minor adapting but will not translate into slippage.

[davepk74]

So are you saying that the truck has to get a customed to my driving technique?

[maxwedge]

Only in respect to shift points and firmness, true internal slippage is a different problem.

[davepk74]

well it slips going into second gear around 35-40. i know it is a slip because the rpms go up and the truck doesnt go any faster.
i have never heard of a transmissioon that has to basically have a break in period with a new owner , and his driving technique.

[maxwedge]

Again not true, the adaptive shifting feature is shift firmness and shift points only. This may need a software update, check with a Dealer on TSB's for this, may also have to have the trans scanned for slippage errors.

[GMMerlin]

Originally Posted by davepk74

well it slips going into second gear around 35-40. i know it is a slip because the rpms go up and the truck doesnt go any faster.
i have never heard of a transmissioon that has to basically have a break in period with a new owner , and his driving technique.

A slip on shift is usually caused by a hydraulic problem, it is possible that the apply oil to the 2-4 band is restricted causing the concern

Here is some info on adaptive shifting
The 4L60-E transmission utilizes a line pressure control system during upshifts to compensate for the normal wear of transmission components. By adjusting the line pressure, the PCM can maintain acceptable transmission shift times. This process is known as "adaptive learning" or "shift adapts" and is similar to the closed loop fuel control system used for the engine.

In order for the PCM to perform a "shift adapt," it must first identify if an upshift is acceptable to analyze. For example, upshifts that occur during cycling of the A/C compressor or under extreme throttle changes could cause the PCM to incorrectly adjust line pressure. When an upshift is initiated, a number of contingencies, such as throttle position, transmission temperature, and vehicle speed, are checked in order to determine if the actual shift time is valid to compare to a calibrated desired shift time. If all the contingencies are met during the entire shift, then the shift is considered valid and the adapt function may be utilized if necessary.

Once an adaptable shift is identified, the PCM compares the actual shift time to the desired shift time and calculates the difference between them. This difference is known as the shift error. The actual shift time is determined from the time that the PCM commands the shift to the start of the engine RPM drop initiated by the shift. If the actual shift time is longer than the calibrated desired shift time, a soft feel or slow engagement, then the PCM decreases current to the pressure control (PC) solenoid in order to increase line pressure for the next, same, upshift under identical conditions. If the actual shift time is shorter than the calibrated desired shift time, a firm engagement, then the PCM increases current to the PC solenoid in order to decrease line pressure for the next, same, upshift under identical conditions.

The purpose of the adapt function is to automatically compensate the shift quality for the various vehicle shift control systems. It is a continuous process that will help to maintain optimal shift quality throughout the life of the vehicle

[davepk74]

i took the truck in and there is a faulty valve body in the trans and the clutches are all burnt up therefore the dealer is overhauling the transmission at no cost to me. I thought these trucks are supposed to be good trucks, i think it is a piece of crap now that it only has 45,000 miles on it and the trans took a dump. I will never buy another Envoy again just because of this problem I am having with the truck.

[GMMerlin]

Originally Posted by davepk74

i took the truck in and there is a faulty valve body in the trans and the clutches are all burnt up therefore the dealer is overhauling the transmission at no cost to me. I thought these trucks are supposed to be good trucks, i think it is a piece of crap now that it only has 45,000 miles on it and the trans took a dump. I will never buy another Envoy again just because of this problem I am having with the truck.

These are good vehicles..you purchased a USED vehicle with 45000 miles...it is questionable at best as to the possible abuse the previous owner put it through

[davepk74]

just letting you all know that the truck is all fixed. It has a brand new transmission in it and runs like a champ, and the best thing is it was all covered under warranty and i didnt even have to come up with my deductable which would have been $100.00