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.
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.
|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.
|1||Auxiliary coolant pump|
|Kl. 31L||Load ground|
|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.
|1||Pressure||2||Characteristic curve at 12 V rated voltage|
Please observe the following specification data for the auxiliary coolant pump:
|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|
Failure of the componentFailure 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