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.
This symptom table aids in the diagnosis of a failed power take-off (PTO) solenoid engagement. This diagnostic does not expose a mechanical condition with the PTO itself. Voltage is supplied at all times through the cruise fuse to the secondary side of the relay. When the relay is energized, the contacts close and current is allowed to flow to the PTO solenoid. The solenoid has its own external ground. When the ignition switch is in the RUN position, voltage is present at the PTO switch. When the PTO switch is in the ON position, voltage is present at the coil of the relay and at the PCM. If the PCM sees all of the conditions necessary to engage the solenoid, the PCM grounds the primary circuit of the relay.