Chart C-12A Coolant Fan Check (1 of 3)

The cooling fan is totally controlled by the Engine Control Module (ECM) based on inputs from the coolant sensor and fan switch. The fan should run if coolant temperature is greater than 112°C (234°F).

Battery voltage is supplied to the fan relay on terminal D and ignition voltage to terminal C.

Grounding CKT 335 (relay terminal B) will energize the relay and supply battery voltage to the fan motor.

The ECM will remove the ground to CKT 335 if vehicle speed is over 40 MPH.

When A/C is used, the fan control switch mounted in the compressor will open when head pressure exceeds 233 psi (1600 kpa) and this input causes the ECM to ground circuit 335.

If a code 14 or 15 sets, the ECM will turn on the cooling fan.