A/T - Loss of 4th Gear/Busy 3-4 Shifting/TCC Cycling
File In Section: 7 TransmissionBulletin No.: 77-71-77
Date: December, 1997
Subject:
Loss of 4th Gear, Slipping in 4th Gear, Busy 3-4 Shifting or TCC Cycling
(Replace Shift Solenoids)
Models:
1996-97 Chevrolet and GMC C/K, G, P Models
with HYDRA-MATIC 4L8OE Transmission (RPO MT1)
Condition
Some owners may comment about a loss of 4th gear, slipping in 4th gear, busy 3-4 shifting or Torque Converter Clutch (TCC) cycling and no DTC's are setting.
Cause
Shift solenoid leaking hydraulically.
Correction
If normal diagnosis does not provide a correction, follow the solenoid test procedure listed. Replace the shift solenoid if it fails the test. Also verify that the transmission cooling system is operating properly.
Service Information (figure 1)
Starting June 23, 1997 (Julian date 174) all HYDRA-MATIC 4L80-E transmissions are being built with the new solenoid assemblies. The new solenoids will service all 1991 through 1997 4L80-E applications.
The above listed conditions occur mainly on high duty cycle applications and/or when the transmission is operated under high temperature conditions.
Each solenoid may be tested for leaking using the following test:
1. Remove the solenoid from the control valve body. Refer to the Service Manual for the proper procedure.
2. Clamp a piece of 1/2 inch I.D. rubber hose over the fluid inlet end of the solenoid.
3. Connect a wire from one of the solenoid terminals to the negative terminal (ground) of a battery.
4. Apply compressed air to the rubber hose. Do not use air pressure in excess of 120 psi. Excessive pressure will not allow the check ball to seat properly.
5. Connect a wire from the other solenoid to the positive terminal (12 volts) of the battery.
6. Observe the air flow through the solenoid. Replace the solenoid if there is an air leak when the solenoid is energized.
Parts Information
New Part Number Description
10478140 1-2 & 3-4 Shift Solenoid (black)
10478141 2-3 Shift Solenoid (white)
Parts are currently available through GMSPO.
Warranty Information
For vehicles repaired under warranty, use the table.