What causes GM code 56?

Shorted relay or solenoid on the QDM B output circuit Damaged wiring or corroded connector at the ECM Failed relay such as cooling fan, EGR or canister purge Faulty ECM quad driver output

How do I fix GM code 56?

Read codes with a paperclip jumper across ALDL terminals A and B and count flashes List which QDM B devices your model uses and unplug them one at a time Inspect wiring and connectors for shorts to ground or voltage Test each relay and solenoid coil for correct resistance Replace the failed part, clear the code and retest Suspect the ECM only after all outputs test clean

56 Quad Driver Module QDM B Circuit Fault

Q: What does GM code 56 mean?

GM code 56. Quad Driver Module QDM B Circuit Fault. Applies to 1988-1995 C/K trucks, Camaro, Corvette, Caprice.

Make: GM (1982-1995)
Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: 1988-1995 C/K trucks, Camaro, Corvette, Caprice

How to read it

Code 56 reads as 5 flashes, pause, 6 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 56 mean?

56. Quad Driver Module QDM B Circuit Fault. This code sets when your vehicle computer detects quad driver module qdm b circuit fault.

Common causes of 56

Shorted relay or solenoid on the QDM B output circuit
Damaged wiring or corroded connector at the ECM
Failed relay such as cooling fan, EGR or canister purge
Faulty ECM quad driver output

How to fix 56

Read codes with a paperclip jumper across ALDL terminals A and B and count flashes
List which QDM B devices your model uses and unplug them one at a time
Inspect wiring and connectors for shorts to ground or voltage
Test each relay and solenoid coil for correct resistance
Replace the failed part, clear the code and retest
Suspect the ECM only after all outputs test clean