Turn/Hazard/Stop Lights (USA/Canada-Z49)

CIRCUIT OPERATION

Turn Signal Lights Control
The Turn Signal Lights are controlled by the Body Control Module (BCM) through two outputs. One output controls the LH Turn Signal Lights and the other output controls the RH Turn Signal Lights. The BCM will activate the Turn Signal Lights only if the Ignition Switch is in RUN. Ignition RUN position is monitored by the BCM at terminal 3D6 (the ignition 3 input).

The BCM activates the Turn Signal Lights when the BCM LH or RH turn input (terminal 1D4 or 1D5) is grounded through the Turn Signal Switch. When terminal 1D4 (the LH turn input) is grounded the BCM grounds the LH turn relays output at terminal 3C12. The BCM grounds the RH turn relays output at terminal 3C8 when terminal 1D5 (the RH turn input) is grounded.

Turn Flasher
The Turn Flasher turns the Turn Signal Lights on and off by opening the circuit when the current heats it up and closing the circuit when it cools down. An open in the LH or RH turn signal circuit reduces the current flow through the Turn Flasher and the Turn Flasher will not become hot enough to open. The Turn Signal Lights will light continuously.

Turn Signal Lights Power
Battery voltage is applied through Console Fuse Block Fuse B11, CKT 639, the Turn Flasher. CKT 16, the Turn/Hazard Relay contacts between terminals 4 and 3, and CKT 922 to terminal 5 of the LH and RH Front and Rear Turn Signal Relays when the Ignition Switch is in RUN. BULB TEST or START. Battery voltage is applied at all times to the coils of the Turn Relays through Console Fuse Block Fuse D9 and CKT 440. The BCM energizes the LH Front and Rear Turn Relays by grounding the relay coils through CKT 318 at terminal 3C12. The relay contacts close, battery voltage is applied to the LH Turn Signal Lights through CKTs 14 and 18, and the LH Turn Signal Lights turn on. The Turn Flasher turns the lights on and off.

The RH Turn Signal Lights operate similarly to the LH Turn Signal Lights. The BCM grounds the coils of the RH Front and Rear Turn Signal Relays through CKT 319 at terminal 3C8. The relays energize and battery voltage is applied to the RH Turn Signal Lights through CKTs 15 and 19. The Turn Flasher turns the lights on and off.

Turn Signal Indicator
The BCM commands the Turn Signal Indicator in the IPC on and off through the UART data line based on the frequency of the turn signal rate feedback input at BCM terminal 3D3. The BCM turn signal rate feedback input is in parallel with the Turn Signal Lights when the Turn Relays are energized. The turn signal rate feedback input senses the frequency at which the Turn Signal Lights are being turned on and off. The BCM commands the Turn Signal Indicator in the IPC on and off at the same frequency as the turn signal rate feedback input. If the turn signal rate feedback input does not change state for two seconds when Turn Signal operation has been selected, the BCM will command the Turn Signal Indicator on continuously, indicating an open bulb or an open in the wiring.

Hazard Lights
The Hazard Lights are controlled by the Hazard Switch in the Headlight Switch and the BCM. When the Hazard Switch is operated a Hazard Lights request is sent to the BCM through the lighting data line from the Headlight Switch. In response to the Hazard Lights request the BCM activates the LH and RH turn relays outputs and the turn/hazard relay output. The operation of the Hazard Lights is similar to the Turn Signal Lights. The only difference is that the BCM energizes the Turn/Hazard Relay which switches the supply to the Hazard Flasher. Battery voltage is applied to the Hazard Flasher at all times through Console Fuse Block Fuse B13 and CKT 140. This allows the Hazard Lights to operate at all times.

Battery voltage is applied at all times to the Turn/Hazard Relay coil through Console Fuse Block Fuse D9 and CKT 440. The BCM energizes the Turn/Hazard Relay by grounding the relay coil at terminal 3C11 (the turn/hazard relay output) through CKT 665 when the Hazard Lights are requested.

Hazard Flasher
When current flows through the Hazard Flasher element it heats up, closes the switch and the lights turn on. When the switch is closed, all the current passes through the switch, and the element cools down and opens the switch. This sequence continues until current flow through the Hazard Flasher stops.

Hazard Indicator
The BCM commands on the Hazard Indicator in the Analog IPC and the Turn Signal Indicator in the Digital IPC (through the UART data line) in response to the frequency of the turn signal rate feedback input during Hazard Light operation.

The Hazard Lights LED in the Headlight Switch is commanded on by the BCM through the lighting data line during Hazard Lights operation.

Stop Lights
The Stop Lights are controlled by the stop contacts of the Stop/BTSI/Cruise Brake Switch. When the brake pedal is depressed the stop contacts close and battery voltage is applied to the Center High Mounted Stop Lamp and the Tail/Stop filaments of the LH and RH Tail/ Stop-Turn Lamps. The Stop Light Switch Capacitor is for noise and spike suppression when the stop contacts open and close.