Theory Of Operation

The Body Control Module (BCM) receives CAN Bus messages from the Steering Column Control Module (SCCM), requesting Left or Right Turn Lamp illumination. A ground path for the Left and Right Tail Lamp Assemblies is provided through the wiring harness to the body sheet metal.

When requested, the BCM provides a Pulsed Width Modulated (PWM) voltage signal output to the Left or Right Rear Turn Lamp.

INCANDESCENT LAMPS:  When a Left or Right Turn Lamp activation is requested, the BCM provides the PWM output @ 100Hz on the associated driver circuit.

LED LAMPS: 

When a Left or Right Turn Lamp activation is requested, the BCM provides the PWM output @ 200Hz with a voltage signal between 0 - 12 volts to the selected Tail Lamp Assembly through one of the associated driver circuits (as equipped):

• Rear Turn Lamp Driver circuit
• Stop Lamp Driver circuit
• Stop/Turn Lamp Driver circuit

With the ignition on, the BCM provides a diagnostic voltage output to the Left and Right Tail Lamp Assemblies through the Left and Right Lighting Fault Sense circuits. When the Left or Right Turn Lamp is activated, the internal driver of the Tail Lamp Assemblies pulls the Lighting Fault Sense circuit voltage signal low when the Turn Lamps are illuminated. When the Turn Lamps are Off, the Lighting Fault Sense circuit voltage signal from the BCM is above 4 volts.

A failure in the Rear Lighting Fault Sense circuit may be caused by one of the following conditions:

• When the Left or Right Turn Lamps are ON and the voltage on the Lighting Fault Sense circuit is a constant voltage may indicate:
• A poor connection in the harness connector.
• The Lighting Fault Sense circuit is open.
• The Tail Lamp Assembly ground circuit is open.
• The Tail Lamp Assembly is inoperative.

• When the Tail Lamp Assembly harness connector is connected  (back-probing), the Left or Right Turn Lamps are OFF and the voltage on the Lighting Fault Sense circuit is below 4 volts may indicate:
• The Lighting Fault Sense circuit is shorted to ground.
• The Tail Lamp Assembly is internally shorted.
• Water or corrosion in the harness connector/terminal.

• When the Tail Lamp Assembly harness connector is disconnected  and the voltage on Lighting Fault Sense circuit is below 4 volts (with none of the above faults are present) may indicate the BCM is not supplying the diagnostic voltage signal on the Lighting Fault Sense circuit.