Electric Cooling Fan Diagnosis

CIRCUIT DESCRIPTION
Power is supplied to the cooling fan motors through fusible links. The relays are energized when the PCM completes the ground path to the relay coil. The PCM Output Driver Module (ODM) B output 1 is grounded for Fan 1 operation. PCM ODM B output 2 is grounded for Fan 2 operation.

During Fan 1 operation the PCM supplies a ground path for the Fan 1 relay through ODM B output 1. This closes Fan 1 relay contacts and current flows from the battery through the relay and to the puller cooling fan. The puller cooling fan is grounded at the engine block. The PCM commands Fan 1 ON when engine coolant temperature increases above 108°C (226°F). Fan 1 will remain ON until the engine coolant temperature decreases below 103°C (217°F). The PCM also commands Fan 1 ON when A/C refrigerant pressure increases above 1310 kPa (190 psi). Fan 1 will remain ON until the A/C refrigerant pressure decreases below 807 kPa (117 psi).

During Fan 2 operation the PCM keeps Fan 1 energized and supplies a ground path for the Fan 2 relay through ODM B output 2. This closes Fan 2 relay contacts and current flows to the pusher cooling fan. The pusher cooling fan is grounded at the chassis. The PCM commands Fan 2 ON when engine coolant temperature increases above 111°C (232°F). Fan 2 will remain ON until the engine coolant temperature decreases below 108°C (226°F). The PCM also commands Fan 2 ON when vehicle speed is below 77 km/h (48 mph) and A/C refrigerant pressure increases above 1655 kPa (240 psi). Fan 2 will remain ON until the A/C refrigerant pressure decreases below 1310 kPa (190 psi).


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

2. Stored Diagnostic Trouble Codes (That may not illuminate the Malfunction Indicator Lamp) may enable the engine cooling fans.

3. Checks for cooling fan(s) ON all the time condition.

4. Ensures that the PCM, Fan 1 relay, and related wiring can operate the puller fan properly.

5. Ensures that the PCM, Fan 2 relay, and related wiring can operate the pusher fan properly.

59. 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. Refer to PCM Replacement and Programming Procedures in Powertrain Control Module (PCM) and Sensors.