Cooling Fan Functional Check

Cooling Fans And Relays:

CIRCUIT DESCRIPTION:
Power for the fan motors is supplied through the cooling fan fuse in the left Maxi-fuse fuse block. The cooling fan relays are energized when current flows from the cooling fan fuse in the Instrument Panel (IP) fuse block through the relay coils to ground through the PCM. The cooling fan 1 control circuit is grounded for low speed fan operation. The cooling fan 1 and cooling fan 2 control circuits are grounded for high speed operation.

During low speed fan operation the PCM supplies a ground path for the low speed cooling fan relay 1. This closes the low speed relay contacts, allowing current to flow from the battery junction block through the relay contacts to the primary cooling fan. During low speed operation, the ground path for the primary cooling fan is through the series/parallel cooling fan relay and secondary cooling fan motor. The result is a series circuit with both fans running at low speed.

During high speed cooling fan operation the PCM supplies a ground path for the low speed cooling fan relay through the cooling fan 1 control circuit. The PCM also supplies a ground path for the high speed cooling fan relay 3 and the series/parallel cooling fan relay 2 through the cooling fan 2 control circuit. This closes all 3 fan relays. During high speed operation, both the left and the right cooling fans are supplied current from the battery junction block and each fan has a ground path. The PCM will also enable the cooling fans on low speed for 3 minutes after the ignition is turned off when the coolant temperature exceeds 140°C (284°F).

DIAGNOSTIC AIDS
Check for the following conditions:
^ A faulty connection at the PCM, the cooling fan relays, or the cooling fan motors
Inspect the harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections. Use a corresponding mating terminal to test for the correct terminal tension.
^ Inspect the wiring harness for damage. Refer to Testing for Intermittent and Poor Connections in Diagrams.

If the owner noted an overheating problem, determine if the complaint was due to an actual boil-over, the warning indicator light illuminating, or the engine coolant temperature gauge indicating overheating. The gauge accuracy can also be checked by comparing the Engine Coolant Temperature (ECT) sensor reading using a scan tool and comparing its reading with the gauge reading. If the engine is actually overheating, and the gauge indicated overheating but the cooling fan is not coming on, the 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, refer to Engine Overheating in Engine Cooling. Cooling System

The PCM commands the low-speed fans on at 106°C (223°F) and off at 102°C (216°F), and commands the high-speed fans on at 112°C (234°F) and off at 105°C (221°F). With low coolant, the PCM commands the low-speed fans on at 80°C (176°F) and off at 76°C (169°F), and commands the high-speed fans on at 100°C (212°F) and off at 98°C (208°F). With low coolant, the PCM commands the low-speed fans on at 80°C (176°F) and off at 76°C (169°F), and commands the high-speed fans on at 100°C (212°F) and off at 98°C (208°F). When the A/C is requested, the PCM commands the low-speed fans on when the A/C refrigerant pressure is more than 1372 kPa (190 psi), and commands the low-speed fans off at 1218 kPa (177 psi), and commands the high-speed fans on at 1632 kPa (237 psi) and off at 1428 kPa (207 psi). The DIM will command the low-speed fans on at key-off for 3 minutes if the engine coolant temperature exceeds 118°C (244°F).


TEST DESCRIPTION

Diagnostic Chart:

The numbers below refer to the step numbers on the diagnostic table.
2. The PCM will enable the engine cooling fans when certain DTCs are set. Refer to the applicable DTC table before proceeding with this table.
3. Allow the engine coolant temperature to cool to less than 100°C (212°F) before proceeding with diagnosis.