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 4WD LO circuit is used to notify either the powertrain control module (PCM) for gasoline applications or the engine control module (ECM) for diesel applications that the vehicle is in 4WD low range. The applicable control module supplies 12 volts to this circuit. The transfer case shift control module grounds this circuit when the vehicle is in 4WD low range.
This DTC detects a short to ground, short to voltage, or an open in the 4WD LO circuit.