Part 1 of 2

Chart C-12 Part 1 Of 2:

Cooling Fan Control Wiring Schematic:

Relay Center:

CIRCUIT DESCRIPTION
The primary and secondary electric cooling fan(s) are controlled by the Powertrain Control Module (PCM), based on inputs from the Engine Coolant Temperature (ECT) sensor, the A/C control switch, vehicle speed, and state of the A/C pressure sensor. The PCM controls the fan(s) by grounding CKT 335 and/or CKT 473, which energizes the fan control relay, battery voltage is then supplied to the fan motor.

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

1. Using the Tech 1 scan tool, commanding both relays "ON," the cooling fan control driver(s) will close, which should energize the fan control relay(s).
2. If the A/C pressure is above 1696 Kpa (246 psi), both fans should be energized whenever A/C is requested.
3. With A/C clutch engaged and the A/C pressure sensor functioning properly, the primary fan should come "ON" when pressure exceeds about 1310 Kpa (190 psi). This signal should cause the PCM to energize the fan control relay(s).
4. This will determine if the A/C pressure sensor is faulty, or if the PCM or circuitry is faulty.

DIAGNOSTIC AIDS
If the owner comments about an overheating problem, it must be determined whether the comment was due to an actual boil over, or the hot light, or temperature gauge indicated overheating.

If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. The gauge accuracy can also be checked by comparing the engine coolant temperature reading using a scan tool and comparing its display with the gauge reading.

If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not coming "ON," ECT sensor has probably shifted out of calibration and should be replaced.