Diagnostic Aids

If an overheating condition is suspected, check if it is caused by an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.

If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check Engine Coolant Temperature (ECT) sensor temperature using a scan tester. ECT sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system. PCM will command low speed cooling fan operation on at 226°F (108°C) and off at 221°F (105°C). High speed cooling fan operation turns on at 235°F (113°C) and turns off at 230°F (110°C).

Fig 1: Chart C-12, Cooling Fan Circuit Schematic (5.7L - Late Production A/C)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Chart C-12, Cooling Fan Circuit Diagnostic Flow Chart (5.7L - Late Production A/C - 1 Of 4)

Courtesy of GENERAL MOTORS CORP.

Fig 3: Chart C-12, Cooling Fan Circuit Diagnostic Flow Chart (5.7L - Late Production A/C - 2 Of 4)

Courtesy of GENERAL MOTORS CORP.

Fig 4: Chart C-12, Cooling Fan Circuit Diagnostic Flow Chart (5.7L - Late Production A/C - 3 Of 4)

Courtesy of GENERAL MOTORS CORP.

Fig 5: Chart C-12, Cooling Fan Circuit Diagnostic Flow Chart (5.7L - Late Production A/C - 4 Of 4)

Courtesy of GENERAL MOTORS CORP.