What causes GM code 29?

Shorted fourth gear switch or TCC solenoid circuit Damaged wiring along the transmission harness Failed quad driver output inside the ECM Worn overdrive components preventing fourth gear engagement

How do I fix GM code 29?

Confirm the transmission actually shifts into fourth gear on a road test Inspect the transmission connector and harness for damage Test the fourth gear switch and solenoid resistance per the manual Repair external wiring before suspecting the ECM Clear codes and verify fourth gear signal on a repeat drive

29 Quad Driver Module Fourth Gear Circuit Fault

Q: What does GM code 29 mean?

GM code 29. Quad Driver Module Fourth Gear Circuit Fault. Applies to 1988-1995 GM cars with automatic overdrive transmission, Corvette, Camaro.

Make: GM (1982-1995)
Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: 1988-1995 GM cars with automatic overdrive transmission, Corvette, Camaro

How to read it

Code 29 reads as 2 flashes, pause, 9 flashes on the check-engine light. Jump terminals A and B on the ALDL connector with the key off, then turn the key on with the engine off and count the check-engine flashes.

What does GM code 29 mean?

29. Quad Driver Module Fourth Gear Circuit Fault. This code sets when your vehicle computer detects quad driver module fourth gear circuit fault.

Common causes of 29

Shorted fourth gear switch or TCC solenoid circuit
Damaged wiring along the transmission harness
Failed quad driver output inside the ECM
Worn overdrive components preventing fourth gear engagement

How to fix 29

Confirm the transmission actually shifts into fourth gear on a road test
Inspect the transmission connector and harness for damage
Test the fourth gear switch and solenoid resistance per the manual
Repair external wiring before suspecting the ECM
Clear codes and verify fourth gear signal on a repeat drive