Electric Cooling Fan Diagnosis

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
Power for the cooling fan motors comes from the Cooling Fans Maxi-Fuse. The relays are energized when the PCM grounds the fan driver circuits. The PCM Output Driver Module (0DM) B output 1 (low speed fan control circuit) is grounded for Low Speed fan operation. PCM 0DM B outputs 1 (low speed fan control circuit) and 2 (high speed fan control circuit) are grounded for High Speed operation. The cooling fan system on this vehicle consists of a single speed right side cooling fan and a dual speed left side cooling fan. While in low speed operation, CKT 409 supplies battery feed directly to the right side cooling fan motor. The left side cooling fan motor is supplied a feed through a resistor, causing it to run at low speed. When high speed operation is commanded, the right side fan continues to run at low speed; but CKT 532 supplies a feed directly to the left side cooling fan motor, causing it to run at high speed.

The PCM commands low speed fans operation when the following conditions are present:

^ Vehicle speed is less than 58 mph.
^ Engine coolant temperature is above 100°C (212°F).

OR

^ Vehicle speed is less than 40 mph.
^ Intake air temperature is above 9°C (48°F).
^ A/C refrigerant pressure is greater than 190 psi (1300 kPa).

High speed fan operation is commanded when the following conditions are present:

^ Vehicle speed is less than 65 mph.
^ Engine coolant temperature is above 108°C (226°F).

OR

^ Vehicle speed is less than 50 mph.
^ A/C refrigerant pressure is above 260 psi (1800 kPa).

DIAGNOSTIC AIDS
Check for the following conditions:

^ Poor connection at the PCM, cooling fan relays, or cooling fan motors.

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

^ Damaged harness.

Inspect the wiring harness for damage.

TEST DESCRIPTION
Number(s) below refer to the step number(s) on the Diagnostic Table.

2. Stored diagnostic trouble codes may affect engine cooling fan operation. This diagnostic table may lead to improper diagnosis and replacement of good parts if diagnostic trouble codes are present.

6. Ambient temperature must be greater than 9°C (48°F) before the PCM will enable the cooling fans due to A/C request. The PCM will enable the cooling fans if A/C refrigerant pressure increases regardless of ambient temperature.

44. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.