Electric Cooling Fan Diagnosis

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

Power for the cooling fan motors comes from the Cool Fan 1 and Cool Fan 2 Maxi fuses (R). The relays are energized when the PCM grounds the fan relay control circuits. The PCM Output Driver Module (ODM) B output 1 (low speed fan control circuit) is grounded for low speed fan operation. PCM ODM 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 two speed dual speed cooling fans. While in low speed operation, CKT 409 supplies battery positive voltage directly to the right side cooling fan motor. The left side cooling fan motor is supplied battery positive voltage through the right side cooling fan motor, causing both cooling fans to run at low speed. When high speed operation is commanded, the right side fan and left side fans are supplied with their own battery positive voltage feed and ground, causing both cooling fans to run at high speed.

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

^ Engine run time is greater than 3 seconds.

^ Vehicle speed is less than 53 mph.

^ Engine coolant temperature is greater than 100°C (212°F).

OR

^ Vehicle speed is less than 53 mph.

^ Intake air temperature is greater than 4°C (39°F).

^ A/C refrigerant pressure is greater than 190 psi (1300 kPa).

For high speed cooling fan operation, the PCM delays control of the high speed cooling fan relay for 6 seconds. The 6 second delay ensures that the cooling fan electrical load will not exceed the capacity of the system. High speed fan operation is commanded when the following conditions are present:

^ Vehicle speed is less than 65 mph.

^ Engine coolant temperature is greater than 106°C (226°F).

OR

^ Vehicle speed is less than 65 mph.

^ A/C refrigerant pressure is greater than 244 psi (1689 kPa).

DIAGNOSTIC AIDS

Check for the following condition(s):

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

^ 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 fans 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 above 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.

7 7. 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.