Chart C-12B Coolant Fan Functional Check (No Low Speed)

Chart C-12B - Coolant Fan Functional Check (No Low Speed):

Wiring Diagram for Coolant Fan Functional Check:

CHART C-12B - COOLANT FAN FUNCTIONAL CHECK (NO LOW SPEED)

Circuit Description:

On V08 (Heavy Duty Cooling) systems, the two coolant fans are energized through one low speed and two high speed relays. On standard cooling applications, one fan, one low speed relay and one high speed relay are used.

Power for the fan(s) comes through the fusible link to terminal "1" on all relays. The relays are energized when current flows to ground through the activation of the A/C pressure and coolant temperature switches, and/or the ECM.

Low Speed Relay - The Low Speed Relay is energized by the ECM or the A/C pressure switch. The ECM energizes the relay through Terminal "D2" when the coolant temperature reaches 98°C (208°F) and vehicle speed is below 45 mph. The Low Speed Relay is also energized through the A/C pressure switch through terminal "B" when refrigerant pressure reaches 1034 kPa (150 psi).

High Speed Relay - The High Speed Relay is energized by the A/C high pressure and coolant override switches. If the A/C refrigerant pressure reaches 1896 kPa (275psi) or the coolant temperature reaches 108° (226 °F) the High Speed Fan Relay is energized. The ECM has no control of the High-speed Fan Relay.

Pusher Fan Relay - The Pusher Fan is installed as part of the heavy duty cooling package (V08) and is turned "ON" anytime the high speed fan is running. When the A/C pressure reaches 1896 kPa (275 psi) or the coolant temperature reaches 108°C (226°F) both fans are energized. The ECM has no control of the Pusher Fan Relay.




Test Description: The following numbered steps correspond with the step numbers on the diagnostic chart.

1. Test light should be on because harness terminal "5" has battery voltage with Ign. switch turned "ON".

2. Test light should be "ON" for 3 seconds and "OFF" for 3 seconds as E009 cycles fan "ON/OFF" at 3 second intervals.

3. Jumpering Harness terminals "1" and "4" bypasses the relay. If fan runs, the relay is faulty.

4. If CKT 2 was open the test light would be "OFF".

5. Cycling of the test light proves CKT 532 and 804 are OK so fan motor is faulty.