High Beam Relay: Description and Operation

ISO Micro Relay:

The headlamp high beam relay is a conventional International Standards Organization (ISO) micro relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. This relay is contained within a small, rectangular, molded plastic housing and is connected to all of the required inputs and outputs through five integral male spade-type terminals that extend from the relay base plate.

The headlamp high beam relay is located in the Junction Block (JB) This relay is omitted from vehicles manufactured for sale in Canada, which have a Daytime Running Lamp (DRL) solid state relay installed in the JB that also performs the high beam relay function.

The headlamp high beam relay cannot be adjusted or repaired and, if faulty or damaged, it must be replaced with a new unit.

The headlamp high beam relay is an electromechanical switch that uses a low current input from the Body Control Module (BCM) to control a high current output to the headlamp high beam filaments. Within the relay are an electromagnetic coil, a movable contact and two fixed contact points. A resistor is connected in parallel with the coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the field of the relay coil collapses.

The movable common supply contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This field draws the movable contact point away from the normally closed contact, and holds it against the normally open contact. When the relay coil is de-energized, spring pressure returns the movable contact back against the normally closed contact.

The inputs and outputs of the headlamp high beam relay include
- Common Supply Terminal (30) - The common feed terminal is connected to a fused B(+) circuit at all times.
- Coil Ground Terminal (85) - The common feed terminal is connected to a fused B(+) circuit at all times.
- Coil Battery Terminal (86) - The coil battery terminal is connected to a control output of the Body Control Module (BCM) and to the momentary optical horn (flash-to-pass) output of the multi-function switch through a high beam relay control circuit The BCM and/or the multi-function switch controls headlamp high beam operation by controlling a ground path through this circuit.
- Normally Open Terminal (87) - The normally open terminal is connected to the headlamp high beam filaments through the high beam relay output circuit and provides battery voltage to the headlamp high beams whenever the relay is energized.
- Normally Closed Terminal (87A) - The normally closed terminal is not connected in this application, but will have battery voltage present whenever the relay is de-energized.

The headlamp high beam relay can be diagnosed using conventional diagnostic tools and methods. Refer to the appropriate wiring information.