Auxiliary coolant pump

The auxiliary coolant pump is only installed with specific engine versions.

The auxiliary coolant pump serves to make sure that the coolant flow rate needed in the heater circuit is maintained (for combustion engines, among others, even at low engine speeds):

If an auxiliary heater has been installed, the auxiliary coolant pump will not be present. The function is assumed by the circulating pump on the auxiliary heating.

Functional description

The electric auxiliary coolant pump is a single stage radial pump.

The coolant enters the auxiliary coolant pump in an axial plane, while the discharge is radial relative to the impeller's rotational axis.

The auxiliary coolant pump is powered by a brushless electric motor. The IHKA control unit relays activation and deactivation commands to the auxiliary coolant pump in the form of messages on the K-CAN. The junction box electronics (JBE), the front electronic module (FEM) or the Body Domain Controller (BDC) controls the auxiliary coolant pump.

Item Explanation Item Explanation
1 Coolant inlet 2 Coolant outlet
3 Auxiliary coolant pump (without bracket) 4 three‐pin plug connection

Structure and inner electrical connection

A 3-pin plug connects the auxiliary coolant pump to the onboard electrical system.

Item Explanation Item Explanation
1 Auxiliary coolant pump

Pin assignments

Pin Explanation
Kl. 31L Load ground
U Supply voltage
1 pin not used.

Characteristic curve and setpoint values

The auxiliary coolant pump's speed is not controlled. The coolant pump operates at a rotation rate of roughly 2800 rpm.

Item Explanation Item Explanation
1 Pressure 2 Characteristic curve at 12 V rated voltage
3 Volumetric flow

Please observe the following specification data for the auxiliary coolant pump:

Variable Value
Speed (operating point) Approx. 2800 rpm
Volumetric flow rate (minimum) 720 l/h
Voltage range 9 to 16 V
Supply voltage 12 V
Maximum current consumption in normal operating mode 1.2 A to 1.4 A

Temperature range of coolant temperature

(max. 135 °C for one hour)

-40 to 125 °C
Temperature range -40 to 120 deg C

Diagnosis instructions

Failure of the component

Failure of the auxiliary coolant pump is accompanied by the following symptoms:
  • Fault code entry in the junction box electronics (JBE), front electronic module (FEM) or Body Domain Controller (BDC)

Function check of the component

The diagnosis system can be used to check operation of the auxiliary coolant pump.

Path: Function network > Body > Heating and air conditioning function > Climate control, Temperature control > Auxiliary coolant pump

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