Code 56, Quad-Driver "B" Fault 3.8L

PCM uses Quad-Driver Modules (QDMs) to control several devices. When PCM is commanding a component on, voltage of output circuit will be low (near zero volts). When PCM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being controlled. PCM has an internal fault line for each quad-driver module. Fault line status can be displayed on a scan tester. If PCM detects an output voltage other than what is expected on fault line, PCM will set Code 56.

1. PCM does not know which controlled circuit caused Code 56 to set. This chart will check each circuit to determine which is at fault. If other QDM-related codes are present, use those charts first.
2. If QDM "B" related symptoms are present, checks on Code 56 chart should isolate cause of fault.
3. These steps help determine which circuit is out of specification.
4. This step helps determine if problem is circuit or component.