Cooling Fan Functional Check

Diagnostic Chart:

CIRCUIT DESCRIPTION
The cooling fans are controlled by the PCM based on various inputs. Ignition voltage is supplied to all 3 cooling fan relay coils. The PCM controls the low speed cooling fan relay by providing the ground path. The PCM controls the series/parallel and the high speed cooling fan relays together by providing a ground path. The left and right cooling fans are connected in series. This will enable both tans on low speed when the low speed relay is energized. When all three fan relays are energized, both fans will operate at high speed. The high speed is possible because the fan relays are wired in a parallel circuit. When the PCM detects that certain DTCs are set, the PCM will enable the cooling tans. 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 poor 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 poor terminal to wire connection. Use a corresponding mating terminal to test for proper terminal tension.
^ A damaged harness.
Inspect the wiring harness for damage. Refer to testing for Intermittent and Poor Connections in Diagrams.

If the owner complained of an overheating problem, determine if the complaint was due to an actual boil over, the warning indicator light illuminated, or the engine coolant temperature gauge indicated overheating. The gauge accuracy can also be checked by comparing the engine coolant temperature (ECT) sensor reading using a scan tool and comparing the 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.

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

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

Refer to Engine Cooling Schematics Cooling Fans and Relays for a wiring diagram.