Backup Lamp: Description and Operation

BACKUP LAMPS

AUTOMATIC TRANSMISSION
The underhood fuse block supplies battery positive voltage to the coil and switch terminals of the BACKUP LAMPS relay. When the transmission is placed in the REVERSE position, the transmission control module (TCM) sends message via GMLAN to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM grounds the backup lamp relay control circuit of the backup lamps relay. This energizes the backup lamps relay, closing the switch side contacts and provides battery voltage to the BACKUP LAMPS fuse through to the backup lamps. The backup lamps are permanently grounded at G402. With both power and ground the backup lamps illuminate. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the TCM via GMLAN serial data requesting the BCM to remove ground from the backup lamp relay control circuit. This opens the backup lamps relay switch contacts turning OFF the backup lamps.

MANUAL TRANSMISSION
Battery voltage is applied to the backup lamp switch when the ignition switch is in the RUN or CRANK positions. When the transmission is placed in the REVERSE position, the backup lamp switch provides battery voltage to the backup lamps. The backup lamps are permanently grounded at G402. With both power and ground the backup lamps illuminate. Once the driver moves the gear selector out of the REVERSE position, the backup lamp switch contacts open and the backup lamps turn OFF.