Code B420 - Relay Circuits: Notes

The BCM operates twilight, retained accessory power, high/low beam and courtesy light relays by providing a ground for the coils. When relay or relays are on, BCM output will be low and when relays are off, BCM output will be high. Code B420 will set if ignition is on and output voltage at BCM is low when a high has been commanded.

1. To determine which system has failed, select BCM output function in diagnostics. As individual outputs cycle on and off, observe their actual operation.