Chart C-12 Coolant Fan Control Circuit

Chart C-12A: Electric Cooling Fan Control Circuit Diagnosis:

Chart C-12 - Part 2 Of 2:

Cooling Fan Circuit:

CIRCUIT DESCRIPTION
The cooling fans are controlled by the Powertrain Control Module (PCM) based on various inputs. Battery voltage is supplied to the primary fan relay on terminal "C4", and secondary fan relay on terminal "C1". Ignition voltage is supplied to terminal "B4" of the primary and "B1" of the secondary fan relay. Grounding CKT 335 (relay terminal "C6") will energize the primary cooling fan relay (Fan 1) and supply battery voltage to the primary cooling fan motor. Grounding CKT 473 (relay terminal "C3") will energize the secondary cooling fan relay (Fan 2) and supply battery voltage to the secondary fan motor.
When certain Diagnostic Trouble Codes (DTCs) are set, the PCM will enable the cooling fans.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. With the output/field service enable terminal grounded at DLC, the cooling fan control driver(s) will close, which should energize the fan control relay(s).
2. The cooling fans should come "ON" anytime A/C system is operating. Engine coolant temperature must be below 100°C (212°F) when performing this step.
3. Comparing the Tech 1 (or equivalent) Scanner pressure and manifold gage set pressure will determine if the A/C refrigerant pressure sensor is out of range. An out of range A/C refrigerant pressure sensor can cause the cooling fans to operate at the wrong times.

DIAGNOSTIC AIDS
If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, or the warning indicator light, or engine coolant temperature gage indicated overheating.

The gage accuracy can also be checked by comparing the Engine Coolant Temperature (ECT) sensor reading using a Tech 1 (or equivalent Scan tool) and comparing its reading with the gage reading.

If the engine is actually overheating and the gage indicated overheating, but the cooling fan is not coming "ON," the Engine Coolant Temperature (ECT) sensor has probably shifted out of calibration and should be replaced.

If the engine is overheating and the cooling fans are "ON," the cooling system should be checked.
The PCM will command fan 1 "ON" at 107°C (225°F) and "OFF" at 103°C (217°F) and, fan 2 "ON" at 111°C (232°F) and "OFF" at 107°C (224°F).