Radiator Cooling Fan Motor Relay: Description and Operation

CIRCUIT OPERATION

EARLY PRODUCTION

Two Coolant Fans are provided. They are wired in parallel so they both operate whenever cooling is required.

The ECM has two Coolant Fan Control outputs, one for high speed and one for low speed. When the ECM's low speed output is turned on at C2 terminal A11, it grounds the coil of the Low Speed Coolant Fan Relay. The Relay closes completing a circuit to the Coolant Fans. The Coolant Fan Resistor drops the voltage to both Coolant Fans since they are wired in parallel. Both Coolant Fans run at low speed. High speed operation is similar and involves grounding C2 terminal B8, the ECM high speed out-put, and the High Speed Coolant Fan Relay coil. The Coolant Fan Resistor is not used for high speed operation.

The ECM controls its Coolant Fan outputs based on signals received from the Coolant Temperature Sensor and the Refrigerant High Side Temperature Sensor. The Coolant Temperature Sensor is wired directly to the ECM. The Refrigerant High Side Temperature Sensor is wired to the BCM. Its temperature signal is processed by the BCM and sent over a Serial Data Line to the ECM in digital form.

LATE PRODUCTION

Operation is similar to that of early production vehicles. The exception is that the RH Coolant Fan always operates at high speed. Only the LH Coolant Fan changes between low and high speeds.