Code 28 - Quad-Driver No. 3 Error (5.7L "F" Body): Notes

ECM uses Quad-Driver Modules (QDMs) to control several devices. When ECM is commanding a component on, voltage of output circuit will be low (near zero volts). When ECM 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 activated. ECM has an internal fault line for each quad-driver module. Fault line status can be displayed on a scan tester. If ECM detects an output voltage other than what is expected on fault line, ECM will set Code 28; however, ECM will not turn on SERVICE ENGINE SOON light.

1. Code 28 will set if ECM detects wrong voltage on fault line for 3 seconds. This step helps determine which QDM-driven component may have set Code 28.
2. This step helps check for a partially shorted coil which would cause excessive current draw. Excessive current draw will be detected on fault line and set this code. If excessive current draw is present, check circuit, and replace defective wiring or component.
3. This step will help determine if problem is related to component, wiring or ECM.