Low Speed Fan Control Relay Circuit

WHEN MONITORED
With the ignition key ON and battery voltage greater than 10 volts.

SET CONDITION
An open or shorted condition is detected in the low speed radiator fan relay control circuit.

THEORY OF OPERATION
PCM controls the low speed operation of the radiator fan through the low speed relay ground circuit.

- One side of the relay control coil is supplied with +12 volts when the ignition switch is turned to the RUN position.

- The circuit is completed when the other side of the relay coil is grounded by the PCM.

PCM activation of the low speed fan depends on coolant temperature, and A/C head pressure.

- The relay will be grounded when the temperature is above a predetermined value (2100 °F is typical), or when A/C head pressure is above 209 psi, provided the temperature is not too high.

- The ground will be removed when the temperature drops to a predetermined value (1990 °F is typical), and when the pressure drops below 125 psi.

PROBABLE CAUSES
- Relay Coil Open Or Shorted
- Fused Ignition Switch Output Circuit Open
- Low Speed Radiator Fan Relay Control Circuit Open Or Shorted
- Inoperative Circuit Driver In Powertrain Control Module