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Home >> Chevrolet >> 1995 >> Corvette Base, 2D Convertible, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> ECM/Pcm Code Charts >> Code 77, Primary Cooling Fan Driver >> Test Description
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Test Description

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. Even if the fan does not operate, listen for an audible click from relay.
  2. 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.
  3. 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
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Fig 2: Code 77 Diagnostic Flow Chart (Corvette) Primary Cooling Fan Driver
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