Code B420, Twilight Relays Circuit: Notes

If the headlight and parking lights did not cycle on and off when BO05 was selected, then this is the system that set Code B420

1. Checks to see if the fault is due to an open circuit or a short to ground in the circuit. If the headlights and parking lights are always on, there is a short to ground in control circuit. If the headlights and parking lights never turn on, there is an open in one of the circuits.
2. Checks to see if the sort to ground is due to the circuit or BCM.
3. Checks to see if the open circuit is due to the circuit or BCM.
4. Checks to see if the open circuit is on the power or ground side of the relay.