BCM Code B420: Courtesy Light Relay Circuit: Notes
WARNING: This page is about a different car, the 1990 Cadillac Seville and 1990 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
If courtesy lights did not cycle on and off when BO04 was selected, then courtesy lights relay Code B420 is set.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
Test Number 1) Check to see if fault is caused by an open circuit or a short to ground. If courtesy lights are always on, then there is a short to ground in control circuit. If courtesy lights are never on, then there is an open in one of the circuits.
Test Number 2) Check to see if short to ground is due to circuit or BCM.
Test Number 3) Check to see if open circuit is due to circuit or BCM.
Test Number 4) Check to see if open circuit is on power side of relay.
Test Number 5) Checks if open circuit is on ground side of relay or if relay is at fault.