Radiator Fan Relay Control Circuit

Name of Code:
Rad Fan Control Relay Circuit

When Monitored:
With the ignition key on, battery voltage greater than 10 volts, and the PCM requests the fans to be turned on.

Set Condition:
An open or shorted condition is detected in the Radiator Fan Control Relay Circuit.

Theory of Operation:
The solid state radiator fan relay controls the operation of the radiator fans. One connector of the relay is supplied with fused B(+) to power the fans. This same B(+) connection powers the internal electronics in the relay. The chassis ground connection (physical attachment to the chassis) on the relay provides a heat sink for the relay and a ground for the internal electronics. The ground connection from the relay connector is a redundant ground for the internal relay electronics. If the relay attachment to the chassis becomes loose or corroded the relay could fail due to its inability to dissipate heat through the chassis attachment. when the relay control circuit is grounded by the PCM, current flows through the relay to the fans. As the engine temperature rises to a preset level, the PCM will start sending a "Pulse Width Modulated" (PWM) ground signal to the relay. The dwell time of the signal will increase or decrease from 30% to 100% based on the engine coolant temperature and A/C pressures. this method of controlling the fans provides an infinitely variable fan speed.

Possible Causes:
- Relay Failure
- Fused B(+)
- Radiator fan relay control circuit open or shorted
- PCM Failure
- Connector terminals
- Connector Wires