Faulty Auxiliary Coolant Pump Relay
Blocked pump control passage
Faulty Auxiliary Coolant Pump
Auxiliary Coolant Pump harness is open or shorted
Auxiliary Coolant Pump circuit poor electrical connection
Engine Light ON (or Service Engine Soon Warning Light)
The auxiliary coolant pump and cooling fan system provides a measure of prevention against fuel vaporization due to excessive engine temperatures. The Engine Control Module (ECM) commands the auxiliary or after boil coolant pump ON when the engine coolant temperature exceeds a calibrated value after engine shut down. The ECM applies ground to the coil side of the auxiliary pump relay. This energizes the coil and applies voltage directly to the pump motor through the switch side of the relay. When the auxiliary coolant pump is activated, coolant is drawn from radiator and pumped into the engine through a tee in the engine coolant inlet pipe. As the colder temperature coolant is drawn into the engine warmer coolant is expelled from the engine and back to the radiator. Removing high temperature coolant from the engine after shut down helps prevent vaporization of the fuel that remains in the fuel injectors and fuel rail during a hot soak.