Headlamp Washer System Operation

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The body control module controls the headlamp washer pump using a programmed pulse type wash sequence. The pulse washing sequence is a wash cycle for a programmed amount of time followed by a programmed amount of delay time to let the water soak which is then followed by another wash cycle for a programmed amount of time. The headlamp washer pump is controlled by the body control module through the headlamp washer relay. The headlamp washer switch signal circuit is supplied a 12-volt reference through a resistor then monitored within the body control module. The headlamp washer switch is open when in an inactive state. When the headlamp washer switch is activated the signal circuit is closed to ground. When the headlamp washer switch signal circuit is closed to ground the reference voltage is dropped across the resistor within the body control module. The low voltage on the headlamp washer switch signal circuit indicates to the body control module the switch status is active. Battery positive voltage is supplied to the coil and switch sides of the headlamp washer relay. When a headlamp wash request is active the body control module energizes the headlamp washer relay by grounding the relay coil through the headlamp washer relay control circuit. When the relay is energized battery positive voltage to the relay switch is supplied to the washer pump control circuit.