Precharge pump

The precharge pump is activated via the precharge pump positive relay and the precharge pump negative relay integrated in the control unit for traction control.

Possible cause(s) of fault:

• The voltage supply for the precharge pump positive relay is interrupted (fuse, connector, cable)
  
• The ground connection for the precharge pump negative relay is interrupted
  
• Cables between the control unit for traction control and precharge pump are defective
  
• One relay or both relays are defective
  
• The precharge pump is defective
  

Storage condition(s):

• The electrical supply of the precharge pump is monitored continuously.
  

Troubleshooting procedure:

• Check of the power supply of the precharge pump positive relay (pin 2, terminal 30)
  
• Check of the ground connection of the precharge pump negative relay (pin 1)
  
• Check of the cables between the control unit for traction control and precharge pump.
  
• Attach the adapter between the control unit for traction control and precharge pump and activate the precharge pump via the service functions.
  If there is no voltage (vehicle voltage) on activation, the control unit for traction control must be replaced.
  If there is voltage (vehicle voltage) on activation, the precharge pump must be replaced.
  

Note

• Renewing the control unit, see Service functions
  
• Precharge pump replacement, see Service functions/Ventilation DSC Hydraulics