Auxiliary Coolant System Pumps

Some engines will include an auxiliary coolant system pump that is PCM controlled. This is a second cooling pump in the main cooling loop. It is a low power electrically controlled pump which is used to provide engine coolant flow under conditions when the engine is not running and the main mechanical cooling pump is inactive. These auxiliary pumps can be used for two primary purposes: 1) to provide coolant flow through the cabin heat exchanger (heater core) which generates heat for the vehicle cabin (stop/start equipped vehicles), and 2) to provide coolant flow to engine components for the purposes of component protection after the engine is shut-off. On turbo equipped vehicles, engine coolant is used to cool the turbo system bearings resulting in a thermal transfer of heat into the coolant. After-run coolant flow may be required to prevent localized coolant boiling that can damage some cooling system components (particularly the degas bottle).

Coolant Pump "A" 

"A" is defined as "High Temp Loop Aux Pump - Cabin Heating" and refers to the auxiliary pump in the primary coolant loop which supplies the heater core for cabin heating. It is used on stop/start applications and HEV/PHEV applications.

The auxiliary cooling pump diagnostics include circuit checks for Open (P2600), short-to-power (P2603), short-to-ground (P2602), and a functional performance check (P2601).

Coolant Pump "B" 

"B" is defined as High Temp Loop Aux Pump - Component Cooling #1" and refers to the auxiliary pump in the secondary coolant loop which supplies the CAC and turbo.

The auxiliary cooling pump diagnostics include circuit checks for Open (P261A), short-to-power (P261D), short-to-ground (P261C), and a functional performance check (P26B1).