Code B420: Courtesy - Twilight Light Relay Circuits: Notes

The BCM operates the twilight sentinel (if equipped), retained accessory power, HI/LO beam and courtesy lamp relays by providing grounds for coils. When relay(s) are on, BCM output will be low and when relay(s) are off, BCM output will be high.

Code B420 will set if output voltage at BCM is high when a low has been commanded, or output voltage is low when high has been commanded. The Reatta will not be equipped with twilight sentinel and only uses one relay for HI/LO beam control.

Test Number 1)  To determine which system has failed (courtesy lamps, twilight, if equipped, HI/LO beams, or retained accessory power), select BCM output function in diagnostics. As individual outputs cycle on and off, observe their actual operation.