Test Description

WARNING: This page is about a different car, the 1995 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Test numbers refer to numbers on diagnostic chart.

Even if the fan does not operate, listen for an audible click from relay.
This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.

Fig 1: Code 77 Schematic (Corvette) Primary Cooling Fan Driver

Fig 2: Code 77 Diagnostic Flow Chart (Corvette) Primary Cooling Fan Driver