Part 2 of 2

Chart C-12 Coolant Fan Control Circuit Diagnosis (Part 2 Of 2):

Coolant Fan Control Schematic:

CIRCUIT DESCRIPTION
The electric cooling fan is controlled by the Powertrain Control Module (PCM), based on inputs from the Engine Coolant Temperature (ECT) sensor, A/C request, A/C refrigerant fan request switch and vehicle speed. The PCM controls the fan(s) by grounding CKT 335 and CKT 473, which energizes the fan control relay(s). Battery voltage is then supplied to the fan motor(s).
The PCM grounds CKT 335 (puller fan relay), when coolant temperature is approximately 106°C (223°F), or when A/C has been requested, and the A/C refrigerant fan request switch opens with high A/C pressure, about 200 psi (1380 kPa).
The pusher fan relay is grounded by the PCM when coolant temperature is approximately 110°C (217°F) and/or puller fan is "ON" for A/C pressure.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. 12 volts should be available to both terminals "87" and "85," when the ignition is "ON."
2. This test checks the ability of the PCM to ground CKT 335 and CKT 473. The Malfunction Indicator Lamp (MIL) (Service Engine Soon) should also be flashing at this point. If it isn't flashing, see Chart A-2 No DLC Data or DTC 12 - MIL "ON" Steady under A Charts. Chart A-2 No DLC Data or DTC 12 - MIL ON Steady
3. This test checks to see if the coolant puller and pusher fan relay (CKTs 409 and 532) are open. Jumpering terminals "87" and "30" bypasses the relay, which should cause the fans to run if fan motors and wiring are OK.

DIAGNOSTIC AIDS
If the owner complained of an engine overheating problem, it must be determined if the complaint 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 or sending unit accuracy can also be checked by comparing the ECT sensor reading using a Tech 1 scan tool and comparing its reading with the gauge reading.
If the engine is actually overheating and the gauge indicates overheating but the cooling fan is not coming "ON" and the Tech 1 scan tool indicates normal readings, the ECT sensor has probably shifted out of calibration and should be replaced.
If the engine is overheating and the cooling fan is "ON," the cooling system should be checked.