Code B420, Relay Circuits (Riviera Only): Notes

Fig 1: Code B420 Flowchart, Relay Circuits

Fig 2: Code B420, Relay Circuits

Fig 3: Code B420 Schematic, Relay Circuits

The BCM operates the twilight sentinel retained accessory power, high beam, low beam, and courtesy light relays by providing a ground for the coils. When the relay(s) are on, the BCM output will be low and when the relay(s) are off, the BCM output will be high.

Code B420 will set if the ignition is on and the output voltage at the BCM is high when a low has been commanded, or the output voltage is low when a high has been commanded.

1. To determine which system has failed (courtesy lights, twilight, high/low beams, or retained accessory power), select the BCM output function in diagnostics. As the individual outputs cycle on and off, observe their actual operation.