GM OBD Trouble Code 56

Quad Driver Module (QDM B) Error

The ECM uses "quad drivers" to control its output devices. Each quad driver is capable of controlling up to four devices.

Fault Code Description

• 56 - Quad Driver Module (QDM B) error

Symptoms

• Improper operation of an ECM-controlled device
  

Common Problems

• Code 56 does not mean there is an internal ECM failure
  
• Code 56 can indicate a circuit problem (open or shorted) in one of the devices controlled by QDM B
  
• Some diagnostic charts may state which devices are controlled by QDM B. In other cases, it may be necessary to monitor which ECM-controlled devices are operating when the Check Engine Light comes on in order to determine which circuit is causing the problem.