Chart C-12 Coolant Fan Control Circuit

Chart C-12 Part 1 Of 2:

Chart C-12 Part 2 Of 2:

Cooling Fan Controls Wiring Schematic:

CIRCUIT DESCRIPTION
Battery voltage to operate the cooling fan is supplied to the cooling fan relay by circuit 2 on cooling fan relay cavities "30" and "85." When the Powertrain Control Module (PCM) grounds circuit 335, the relay is energized and the cooling fan is turned "ON." When the engine is running, the PCM will turn the cooling fan "ON" for any one of the following reasons:
^ Diagnostic Trouble Code (DTC) 14, 15 or 70 is set.
^ Vehicle speed is less than 70 MPH (113km/h).
^ Engine Coolant Temperature (ECT) is 108° C (226° F) or greater, with A/C "ON" or "OFF."
^ A/C refrigerant pressure is greater than 187 psi (1289 kPa).
^ PCM is in backup mode.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

Part 1
1. With the diagnostic terminal grounded, the cooling fan control driver will close, which should energize the fan control relay.
2. If the A/C pressure is above 300 psi (2069 kPa) or circuit is open, the fan would run whenever A/C is requested.
3. With A/C clutch engaged and the pressure sensor is functioning properly, the fan should come "ON" when pressure exceeds about 200 psi (1380 kPa). This signal should cause the PCM to energize the fan control relay(s).
4. This will determine if the A/C refrigerant pressure sensor is faulty or if the PCM or circuitry is faulty.

Part 2
1. Battery voltage should be available to the cooling fan relay cavities "B30" and "B85."
2. This test checks the ability of the PCM to ground circuit 335.
3. If the fan does not turn "ON" at this point, circuit 409 or the cooling fan ground circuit is open, or the cooling fan motor is faulty.

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 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.