GM Service Manual Online
For 1990-2009 cars only

No Fourth Gear, Slips in Fourth Gear

Checks

Causes

Intermediate/Fourth Band & Servo

No apply or slipping

Servo Piston (77)

Broken or binding

Servo Piston Seals (78, 79)

Leaking

Servo Pin (76) and Springs (78, 79)

Binding

Servo Cover (80)

Broken, loose, or leaking

Band (100)

Broken, worn, or out of position

Case (1)

Cracked at the band seat

Band Apply Fluid Routing

Fluid leak and fluid restricting

    • Valve Body
    • Gaskets & Spacer Plate
    • Channel Plate
    • Case
    • Porosity
    • Misalignment
    • Fluid leak across the channels

1-2 Shift Solenoid Valve (305)

    • Stuck OFF
    • Leaking

3-4 Shift Valve (319)

Stuck in the downshifted position

Manual Valve (800)

Misaligned in Manual Third gear

3-4 Accumulator

    • A leak at the piston seal
    • Channel plate or case porosity

3-4 Accumulator Valve (323)

Stuck

Line Pressure

Low pressure (Refer to High or Low Line Pressure )

Direct Clutch

A low capacity will cause a failure in the Fourth gear

PSA

Malfunction (Hydraulic or Electrical)