Chart C-12 Coolant Fan Check

Chart C-12A - Coolant Fan Check:

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

CHART C-12A - COOLANT FAN CHECK

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

1. Grounding the diagnostic test terminal should cause the ECM to ground CKT 535 and the fan should run in low speed.

2. Grounding the temperature switch harness terminal will check CKT 536 and will also check the high side portion of the fan control relay.

3. Checks CKT 533 between the fan control relay terminal "4" and the motor. If the fan does not operate, CKT 533 is open.


4. This step checks to see if the temperature switch is grounding and is grounded when the light comes "ON." The switch should close at 108~C (226~F).

5. If the vehicle is equipped with A/C, the following steps will check the head pressure switches and related wiring from the switch to the fan control relay. If poor A/C performance is noted, the A/C pressure switches should be checked by a qualified A/C repair person. The low speed fan should come "ON" if head pressure exceeds 1036 kPa (150 psi).

Chart C-12B - Coolant Fan Always On:

CHART C-12B - COOLANT FAN ALWAYS ON (CONTINUED FROM CHART C-12A)

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

6. Check to see if CKT 535 is shorted to ground which would keep the relay grounded at all times.

7. Checks to see if CKT 536 is shorted to ground. A light indicates the wire is shorted to ground and the following steps will isolate the short.


8. If the test light is "OFF" after disconnecting, the ECM is shorted internally. Before replacing the ECM be sure and check the resistance value of low speed side of the fan control relay. Replace if resistance is less than 20 ohms. Also, be sure that CKT 535 is not shorted to B+, and check the resistance of the canister purge solenoid, and replace if under 20 ohms.

Chart C-12B - Coolant Fan - No Low Speed Fan:

CHART C-12C - COOLANT FAN - NO LOW SPEED FAN (CONTINUED FROM CHART C-12A)

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

9. Checks for B+ at relay harness connector.

10. Jumpering terminals "1" to "4" bypasses the relay which should cause the fan to run if fan motor and wiring to the motor are good.


11. Grounding the "test" terminal should cause the ECM to ground CKT 535. At this point, the test light should light if the ECM is good and CKT 535 isn't open.

12. This checks for battery + and ground to the fan motor. A test light "ON" at this point indicates a faulty fan motor connection or motor.