Part 1 of 2

Chart C-12 Part 1 Of 2:

Chart C-12 Wiring Diagram:

CIRCUIT DESCRIPTION:
The electric cooling fan is controlled by the ECM based on inputs from the coolant temperature sensor, the A/C pressure sensor 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 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 ECM turns the relay "ON," it will keep it "ON" for a minimum of 25 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 is open, the fan would run whenever the 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.

4. Disconnecting the A/C pressure sensor will cause a Code 66 to set. After finishing this step, be sure to clear codes.

DIAGNOSTIC AIDS:

^ If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over or the hot light (temperature gauge) indicated over heating.
^ If the gauge (light) indicates overheating, but no boil over 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.