Windshield Base/Washer Spray Jet Heaters

Using the E38 as an example for this test, this circuit demonstrates that both heater systems are powered by the same relay.

• The lower portion of the windshield contains heating elements which when powered, prevent the wiper blades from freezing to the glass.
• The washer spray jet heaters are designed to prevent ice from forming on and obstructing the washer nozzles.

The control module monitors the signal from the ambient temperature sensor (K-Bus) and automatically activates the relay in this circuit when

• Ambient temperature is < 38°F (3°C), and 
• The ignition is "ON" and 
• Battery voltage is > 12.2 volts

  If the ambient temperature exceeds 43°F (6°C), the windshield base/washer spray jet heaters are switched off.

  Fig 1: Windshield Base/Washer Spray Jet Heaters Circuit Diagram

  Courtesy of BMW OF NORTH AMERICA, INC.