Chart C-12 Coolant Fan Functional Check

Chart C-12 Cooling Fan Functional Check:

Cooling Fan Functional Check:

CIRCUIT DESCRIPTION
The electric cooling fan is controlled by the Powertrain Control Module (PCM) through the fan relay based on inputs from the engine coolant temperature and, intake air temperature sensors, the A/C control switch, A/C refrigerant pressure sensor and the vehicle speed sensor. The PCM controls the cooling fan by grounding CKT 335 which turns the fan relay "ON."

The fan relay will be commanded "ON" when:

^ Engine coolant temperature is greater than 106°C (223°F).
^ A/C clutch requested.
^ Vehicle speed is less than 35 mph.
^ A DTC is set.

Once the fan is enabled, the PCM will turn the fan "OFF" when:

^ Engine coolant temperature drops below 120°C (248°F).

The cooling fan may be commanded "ON" when the engine is not running.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. With the field service mode activated, the coolant fan control driver should close, which should energize the fan relay control.
2. Test to see if fault is in the wiring to the fan or the fan relay connection.
3. When using breakout box J 39700 use overlay J 39700-112.

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 "temp lamp," or temperature gage indicated overheating.
^ If the gage, or lamp, indicated overheating, but no boil over is detected, the gage or lamp circuit should be checked. The gage accuracy can also be checked by comparing the cooling temperature sensor reading using a scan tool with the gage reading.
^ If the engine is overheating, and the gage indicates overheating, but the cooling fan is not coming "ON," the Engine Cooling Temperature (ECT) sensor has probably shifted out of calibration and should be replaced. See Diagnostic Trouble Code (DTC) 15 chart for a temperature to resistance chart.
^ If the engine is overheating, and the cooling fan is "ON," the cooling system should be checked.