Electric Cooling Fan Circuit Diagnosis: Description

Power for cooling fan motors is supplied through COOL FAN 1 Maxi-fuse (30-amp) and COOL FAN 2 Maxi-fuse (30-amp) in underhood electrical center. Cooling fan relays are energized when current flows from Maxi-fuses through relay coils, then to ground through Powertrain Control Module (PCM). No. 1 cooling fan relay control circuit is grounded for low speed operation. Both fan control circuits and all 3 relays are grounded for high speed fan operation.

During low speed fan operation, PCM supplies a ground path for No. 1 cooling fan relay. As a result, relay contacts close, allowing current to flow from COOL FAN 1 Maxi-fuse through relay coil to cooling fan No. 1 (left side). During low speed operation, ground path for cooling fan No. 1 is through cooling fan relay (5-pin) and cooling fan motor No. 2 (right side). This results in a series circuit with both fans operating at low speed.

During high speed fan operation, PCM supplies 2 ground paths for all 3 cooling fan relays. As a result, relay contacts close in all relays, allowing both cooling fan motors to operate at high speed. Both cooling fans are supplied current from both COOL FAN Maxi-fuses. Each cooling fan motor has a separate ground path when operating in high speed mode.