Principles of Operation

The horn relay is powered on both the control and controlled sides by circuit 1680 (OG/RD). When the horn switch is pressed, the horn relay control circuit 460 (YE/LB) is grounded on one side of the switch through the speed control ground circuit 848 (DG/OG), and by the powertrain control module (PCM) on the other side of the switch. The horn relay is then energized, allowing battery voltage to flow through the horn relay to each horn through circuit 1 (DB), enabling the horns to sound. When the vehicle security system is armed, the vehicle security module provides a momentary ground to the horn relay control circuit 460 (YE/LB) to indicate the system is armed, and a continuous ground when an intrusion is detected. For additional information on the anti-theft system, refer to ANTI-THEFT - PATS . When the tire pressure system is placed in the calibration mode, the tire pressure monitoring system (TMPS) module will provide an intermittent ground through circuit 460 (YE/LB) to alert the technician when each wheel is calibrated. For additional information on the TPMS, refer to WHEELS AND TIRES .