Chart C-12A Coolant Fan Check Less A/C (Single Speed)

Chart C-12A - Coolant Fan Check (Part 1 of 3):

Wiring Diagram for Chart C-12A - Coolant Fan Check:

CHART C-12A - COOLANT FAN CHECK LESS A/C (SINGLE SPEED) PART 1 OF 3

Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if fan runs at all times with ignition "ON."

2. Grounding the test terminal in the ALDL connector should cause the ECM to ground CKT 535. At this point, the fan should run.

3. Grounding the coolant temperature override switch harness to ground should cause the relay to turn "ON" the fan. If the fan runs, the fan control relay and CKT 335 to the coolant temperature override switch are good.


4. Checks to see if coolant temperature override switch operates correctly. Test light should come "ON" at about 108~C (226~F) and the hot light on the instrument panel should come "ON" above 116~C (241~F).

5. Checks to see if coolant fan delay relay works. With coolant temperature override switch harness grounded and ignition "OFF," fan should run about 10 minutes, or until ground jumper is removed.

Chart C-12A - Coolant Fan Check (Part 2 of 3):

CHART C-12A - COOLANT FAN CHECK LESS A/C (SINGLE SPEED) PART 2 OF 3 - CONTINUED FROM CHART C-12A

Test Description: Numbers below refer to circled numbers on the diagnostic chart.

6. This check bypasses the relay and applies B+ direct to the fan through CKT 532. At this point, the fan should run.

7. Checks to see if problem is the control relay, wiring, or ECM.

8. Checks for presence of ignition voltage to relay connector terminal "5".


9. Checks for presence of B + to relay connector terminal "1".

10. Check for an open ground or fan motor circuit. Then checks for open in CKT 532 between relay and motor or faulty motor.

Chart C-12A - Coolant Fan Check (Part 3 of 3):

CHART C-12A - COOLANT FAN CHECK LESS A/C (SINGLE SPEED) PART 3 OF 3 - CONTINUED FROM CHART C-12A

Test Description: Numbers below refer to circled numbers on the diagnostic chart.

11. Checks to be sure constant B+ is at terminals "1" and "2" to the timer relay.


12. Checks to be sure CKT 639 does not have ignition voltage, when the ignition switch is "OFF." If CKT 639 has battery voltage with the ignition "OFF," the timer relay will not turn the fan "ON."

13. Checks to be sure CKT 450 is a good ground.