Relay Circuit (Part 1 of 5)

Code B420 - Relay Circuits (Part 1 of 5):

Wiring Diagram for Code B420 - Relay Circuit:

CODE B420 - RELAY CIRCUIT

Circuit Description:

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

Code B420 will set if the ignition is "ON" and the output voltage at the BCM is HI when a LO has been commanded, or the output voltage is LO when a HI has been commanded.


Test Description:

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


Note on Intermittents:

Since all four groups of relays can cause an intermittent condition, see "Note on Intermittents" for each of the four groups of relays.