Auxiliary coolant pump
An electrically operated auxiliary coolant pump is installed on vehicles with a trailer coupling and/or additional heating. The auxiliary coolant pump ensures that the coolant is circulated when the coolant pump (which is driven by the engine) is not running.
The additional heating uses the auxiliary coolant pump to circulate hot coolant through the heat exchanger and the engine.
On vehicles with a trailer coupling the auxiliary coolant pump is switched on for 6 minutes by the PCM (powertrain control module) if the coolant temperature exceeds 106C when the engine is switched off. This prevents the coolant circuit from overheating. This could happen particularly if the engine is switched off after towing a heavy trailer up a steep hill before there has been sufficient time for cooling.