Turn Signal Lamps

WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START positions. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM responds to the turn signal switch input by sending a serial data message to the Lighting Control Module. The Lighting Control Module responds by applying a pulsating voltage to the front and rear turn signal lamps through there respective control circuits. When a turn signal request is received by the BCM, a serial data message is sent to the Lighting Control Module, the Lighting Control Module sends a serial data message to the instrument panel cluster, the instrument panel cluster responds by indicating to the driver that the respective turn signal has been commanded. The respective turn signal indicator will be pulsed on and off through the instrument panel cluster.

Vehicles with LED turn signals require additional turn signal outage detection circuits that provide turn signal feedback to the Lighting Control Module. The Lighting Control Module uses the feedback information to send a serial data message to the instrument cluster to alert the driver anytime a turn signal fault is detected. If a fault is detected on a turn signal circuit or a turn signal feedback circuit, the turn signals will flash in a rapid manner to alert the driver of the fault.