High Speed Fan Control Relay Circuit

HIGH 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 high speed radiator fan relay control circuit.

Theory of Operation
The high speed radiator fan relay controls the high speed operation of the radiator fan. The relay is located in the power distribution center. 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 Powertrain Control Module (PCM). The PCM grounds the relay control circuit depending on coolant temperature and/or A/C compressor head pressure. When the A/C is off, the relay will be grounded when the temperature reaches 230°F and it will remove the ground when the temperature goes below 221°F. When the A/C is on, the relay will be grounded when the temperature is above 230°F or the head pressure is above 249 psi, and it will remove the ground when the temperature goes below 221°F or the head pressure goes below 229 psi.

Possible Causes
- Relay coil open or shorted.
- Fused ignition switch output circuit open.
- High speed radiator fan relay control circuit open or shorted.
- Inoperative circuit driver in Powertrain Control Module.