Radiator Cooling Fan Motor Relay: Testing and Inspection
Chart C-12 - Coolant Fan Control Circuit:
Wiring Diagram for Coolant Fan Control Circuit:
CHART C-12 COOLANT FAN CONTROL CIRCUIT DIAGNOSIS
(Part 1 of 2)
Circuit Description:
The electric cooling fan is controlled by the ECM based on inputs from the coolant temperature sensor, the A/C fan control switch, and vehicle speed. The ECM controls the fan by grounding CKT 335, which energizes the fan control relay. Battery voltage is then supplied to the fan motor.
The ECM grounds CKT 335 when coolant temperature is over about 106 degrees C (223 degrees F), or when A/C has been requested and the fan control switch indicates high A/C pressure, 200 psi (1380 kPa). Once the ECM turns the relay "ON," it will keep it "ON" for a minimum of 30 seconds or until vehicle speed exceeds 70 mph.
Also, if Code 14 or 15 sets or the ECM is in back up, the fan will run at all times.
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. With the diagnostic terminal grounded, the cooling fan control driver will close, which should energize the fan control relay.
2. If the A/C fan control switch or circuit is open, the fan would run whenever A/C is requested.
3. With A/C clutch engaged, the A/C fan control switch should open when A/C high pressure exceeds about 200 psi (1380 kPa). This signal should cause the ECM to energize the fan control relay.
Diagnostic Aids:
If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boilover or the hot light (temperature gauge) indicated over heating.
If the gauge (light) indicates overheating but no boilover is detected, the gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a "Scan" tool and comparing its reading with the gauge reading.
If the engine is actually overheating and the gauge indicates overheating but the cooling fan is not coming "ON," the coolant sensor has probably shifted out of calibration and should be replaced.
If the engine is overheating and the cooling fan is "ON," the cooling system should be checked.
Chart C-12 - Coolant Fan Control Circuit:
CHART C-12 COOLANT FAN CONTROL CIRCUIT DIAGNOSIS
(Part 2 of 2)
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. 12 volts should be available to both terminal "1" & "5" when the ignition is "ON."
2. This test checks the ability of the ECM to ground CKT 335. The "Service Engine Soon" light should also be flashing at this point. If it isn't flashing, see CHART A-2.
3. If the fan does not turn "ON" at this point, CKT 702 or CKT 150 is open or the cooling fan motor is faulty.