Part 1 of 2

Chart C-12 Cooling Fan Control Circuit Part 1 Of 2:

Cooling Fan Wiring Diagram:

Circuit Description:

The electric cooling fan is controlled by the ECM, based on inputs from the Engine Coolant Temperature (ECT) sensor, the A/C control switches, vehicle speed, and state of the A/C refrigerant pressure sensor. 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 engine coolant temperature is over about 109°C (228°F), or when A/C has been requested and the A/C refrigerant pressure is about 1655 kPa (240 psi). Once the ECM turns the relay "ON," it will keep it "ON" for a minimum of 30 seconds, or until vehicle speed exceeds 113 km/h (70 mph).

Also, if DTC 14 or 15 sets or the ECM is in back up, the primary fan will run at all time.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. With the diagnostic terminal grounded, the cooling fan control driver(s) will close, which should energize the fan control relay(s).

2. If the A/C pressure is above 240 psi (1655 kPa) or circuit is open, the fan would run whenever A/C is requested.

3. With A/C clutch engaged and the A/C refrigerant pressure sensor is functioning properly, the fan should come "ON" when pressure exceeds about 20 psi. Under very cold ambient conditions, the fan will remain "OFF." This signal should cause the ECM to energize the cooling fan control relay.

4. This will determine if the A/C refrigerant pressure sensor is faulty or if the ECM or circuitry is faulty.

Diagnostic Aids:

If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boilover, a hot light or temp gage indicated over heating.

If the gage or light indicates overheating, but no boilover is detected, the gage circuit should be checked.