What causes GM code 27?

Shorted second gear switch or shift solenoid circuit Damaged transmission harness wiring Failed quad driver output inside the ECM Low transmission fluid causing erratic switch signals on some models

How do I fix GM code 27?

Check transmission fluid level and condition first Inspect the transmission connector for fluid intrusion and corrosion Test the second gear switch and solenoid circuits per the service manual Repair wiring faults before condemning the ECM Clear codes and road test to confirm the gear signal returns

27 Quad Driver Module Second Gear Circuit Fault

Q: What does GM code 27 mean?

GM code 27. Quad Driver Module Second Gear Circuit Fault. Applies to 1988-1995 GM cars with automatic 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 transmission, Corvette, Camaro

How to read it

Code 27 reads as 2 flashes, pause, 7 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 27 mean?

27. Quad Driver Module Second Gear Circuit Fault. This code sets when your vehicle computer detects quad driver module second gear circuit fault.

Common causes of 27

Shorted second gear switch or shift solenoid circuit
Damaged transmission harness wiring
Failed quad driver output inside the ECM
Low transmission fluid causing erratic switch signals on some models

How to fix 27

Check transmission fluid level and condition first
Inspect the transmission connector for fluid intrusion and corrosion
Test the second gear switch and solenoid circuits per the service manual
Repair wiring faults before condemning the ECM
Clear codes and road test to confirm the gear signal returns