Voltage Signal: Testing and Inspection

DIAGNOSIS
When certain Diagnostic Trouble Codes (DTCs) are present, the PCM may command the cooling fans to run all the time. It is important to perform the Powertrain On-Board Diagnostic System check prior to diagnosing the engine cooling fans.

If a problem that involves the low speed cooling fan relay control circuit (cooling fan relay # 1 control) exists, DTC P1651 should set. If the problem affects the high speed cooling fan relay control circuit (cooling fan relay # 2 and # 3 control), DTC P1652 should set. A problem with the ECT sensor should set DTC P0117, P0118, P1114, or P1115. Any of these DTCs will affect cooling fan operation and should be diagnosed before using the Electric Cooling Fan Diagnosis table. The System Diagnostic Table "Electric Cooling Fan Diagnosis" should be used to diagnose the PCM controlled cooling fans only if no DTC is set. Testing and Inspection