Radiator Cooling Fan Motor Relay: Description and Operation

ECM Wiring Diagram:

PURPOSE
The electric cooling fans are controlled by the ECM. The ECM determines operation of the independent fans based on A/C head pressure, engine coolant temperature, vehicle speed, and A/C request inputs.

OPERATION
The cooling fans are controlled by the ECM based on various inputs. The primary cooling fan relay is energized by the cooling fan control relay when the cooling fan control relay is de-energized. The primary fan relay will be energized and supply battery voltage to the primary cooling fan motor. Grounding CKT 473 (relay terminal 2) will energize the secondary cooling fan relay (Fan 2) and supply battery voltage to the secondary fan motor.

The A/C cooling fan switch, mounted in the A/C high pressure line, will be grounded when head pressure exceeds 200-300 psi and enable the secondary cooling fan motor.

DIAGNOSTIC NOTES
If a DTC 14, or 15 sets or the ECM is operating in the fuel back-up mode, the ECM will turn "ON" the cooling fans.