Auxiliary Coolant Flow Pump

WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

An auxiliary coolant flow pump is used only on hybrid vehicles to improve engine coolant circulation at low engine speeds or when the engine is OFF.

The auxiliary coolant flow pump will be disabled when any of the following conditions are present:

The climate control module is set to the OFF position.
The ambient temperature is above 32°C (90°F).
The coolant temperature is less than -10°C (14°F).
The engine speed is above 4,000 rpm.

When none of the listed conditions are present, the auxiliary coolant flow pump is controlled by a strategy included in the PCM software. The control strategy monitors the ambient temperature, coolant temperature and engine rpm. As the ambient temperature and/or coolant temperature increase, the auxiliary coolant flow pump will shut down at lower engine speeds. For example, when both the ambient temperature is above 16°C (60°F) and the engine coolant temperature is above 66°C (150°F), the control strategy will shut off the auxiliary coolant flow pump at 2,000 rpm. When both the ambient temperature is above 24°C (75°F) and the engine coolant temperature is above 66°C (150°F), the control strategy will shut off the auxiliary coolant flow pump regardless of engine speed.

To verify auxiliary coolant flow pump operation, allow the vehicle to cool in a cool location. Start the engine and let the engine idle until it shuts down automatically. Select the FLOOR mode on the HVAC module at the highest temperature setting and HI blower speed. If the auxiliary coolant flow pump is inoperative or is not producing adequate coolant flow, the passenger compartment air discharge temperature will quickly decrease and further diagnosis is required. Refer to CLIMATE CONTROL SYSTEM - GENERAL INFORMATION & DIAGNOSTICS -- FUSION, MILAN & MKZ (HYBRID) article. If the auxiliary coolant flow pump is operating normally, the passenger compartment air discharge temperature will remain steady, or slowly decrease.