Auxiliary Coolant Pump

All models except E36/46 use an electrically powered auxiliary coolant pump to ensure that an adequate supply of hot coolant is always available to the heater core(s). The IHKA control module operates the pump directly (E31 uses a relay) by supplying the ground circuit.

Pump "ON" operating criteria (E38 shown as an example):

• Engine coolant temperature > 32°F (supplied via K-Bus on E38/39/46)
• Y-factor > 5%
• Maximum defrost mode selected
• Maximum heating requested
• "REST" function requested

Pump "OFF" when:

• Engine coolant temperature < 32°F and either Y-Factor < 0%, unless other inputs call for pump operation
  Fig 1: Auxiliary Coolant Pump Circuit Diagram

  Courtesy of BMW OF NORTH AMERICA, INC.