High Speed Fan Control Relay Circuit
WHEN MONITOREDWith 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.
- 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 PCM will;
- Ground the relay when the temperature reaches 230°F
- Remove the ground when the temperature goes below 221°F
When the A/C is ON the PCM will;
- Ground the relay when the temperature is above 230°F or the head pressure is above 249 psi
- Remove the ground when the temperature goes below 221 °F or the head pressure goes below 229 psi.
PROBABLE 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