Headlamp Relay: Testing and Inspection

Code B420 - Hi/Lo Beam Relays Circuit (Part 4 of 5):

Wiring Diagram for Code B420 - Hi/Lo Beam Relays Circuit:

CODE B420 - HI/LO BEAM RELAYS CIRCUIT

Circuit Description:

If the HI/LO beams did not cycle on and off when BO06 was selected, then this is the system that set Code B420.






Test Description:

1. Checks to see if the fault is due to an open circuit or a short to ground in the circuit. If the HI beams are always on, then there is a short to ground in control circuit and if the HI beams never turn on, then there is an open in one of the circuits.

2. Checks to see if the short to ground is due to the circuit or the BCM.

3. Check to see if the open circuit is due to the circuit or the BCM.

4. Check to see if the open circuit is on the power or ground side of the relay.


Note on Intermittents:

If an intermittent Code B420 is being set, manipulate the related wiring in output function and watch for relays to cycle.