J2000/Sunbird V6-191 3.1L VIN T MFI (1994)
Cooling Fan Circuit
Circuit Description:
The electric cooling fan is controlled by the PCM based on inputs from the engine coolant temperature sensor, the A/C pressure sensor and vehicle
speed. The PCM controls the fan by grounding CKT 335, which energizes the fan control relay. Battery voltage is then supplied to the fan motor.
The PCM 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 pressure
sensor indicates high A/C pressure, 200 psi (1380 kPa). Once the PCM turns the relay "ON," it will keep it "ON" for a minimum of 25 seconds or
until vehicle speed exceeds 70 mph.
Also, if DTC 14 or 15 sets or the PCM is in backup, the fan will run at all times.
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 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 PCM to energize the fan control relay.
4. Disconnecting the A/C pressure sensor will cause a DTC 66 to set. After finishing this step, be sure to clear DTC(s).
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
gage) indicated over heating.
If the gage (light) indicates overheating but no boilover is detected, the gage circuit should be checked. The gage accuracy can also be checked by
comparing the coolant sensor reading using a Tech 1 scan tool and comparing its reading with the gage reading.
If the engine is actually overheating and the gage indicates overheating but the cooling fan is not coming "ON," the ECT 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.