Circuit Description

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Suburban, and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The ignition relay is a normally open relay. The relay armature is held in open position by spring tension. When ignition switch is turned to run or start position, current will flow through relay coil. A wire connected to other end of relay coil completes path to ground. The electromagnetic field created by relay coil, overcomes spring tension and moves armature allowing relay contacts to close. The closed relay contacts allow current to flow from battery to following fuses: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA fuse, if equipped.

When ignition switch is turned off, electromagnetic field collapses. This action allows spring tension to move armature away from relay contacts, which interrupts current flow to fuses. If ignition relay fails to close, engine will crank, but will not run. The class 2 communications will be available with use of a scan tool.