BCM CODE B420 - RELAY CIRCUITS Cadillac Eldorado IX

BCM CODE B420 - RELAY CIRCUITS

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.

Note. Test number refers to test number on diagnostic chart.

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

Since all 4 groups of relays can cause an intermittent condition, see NOTES ON INTERMITTENTS for courtesy light relay, twilight relays, high/low beam relays, or retained accessory power relays.

Code B420 Schematic, Relay Circuits. Scheme 79

Code B420 Flow Chart, Relay Circuits. Scheme 80

Code B420 Flow Chart, Relay Circuits. Scheme 81