Circuit Description
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The following DTCs are for the starter/generator control module (SGCM) coolant fan relay:
- P1AC1 is for the SGCM coolant fan relay control circuit low voltage condition.
- P1AC2 is for the SGCM coolant fan relay control circuit high voltage condition.
The SGCM controls the coolant fan operation by applying voltage to the coolant fan relay control circuit with an internal solid state device called a driver. When the SGCM is commanding the relay ON, the voltage of the control circuit should be low, near 0 volts. When the SGCM is commanding the relay OFF, the voltage potential of the control circuit should be high, near 12 volts.
The SGCM monitors the relay control circuits for the following conditions:
- Short to ground
- Short to voltage
- An open circuit
If the SGCM detects an improper voltage level on the coolant fan relay control circuit, then DTC P1AC1 or P1AC2 will set and the driver will be disabled.