B420 Relay Coil Circuits

BCM Code B420 (Part 1 Of 5):

BCM Relay Coil Circuit:

DESCRIPTION:

The BCM operates the twilight, 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 "LO" when a "HI" has been commanded.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

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.