Mechanic Glossary

Adblue Pump

An electric pump assembly that pressurizes diesel exhaust fluid (DEF) and sends it to the dosing injector in the exhaust pipe.

The AdBlue pump sits inside or on top of the diesel exhaust fluid (DEF) tank. Its job is to pressurize the fluid to about 70 PSI and send it down the heated line to the injector. The pump assembly also houses a fluid heater, a temperature sensor, and a pressure control valve. When you turn off the engine, the pump runs in reverse, sucking the remaining fluid out of the lines back into the tank to prevent the water-based fluid from freezing and cracking the hoses in winter.

DEF fluid is highly corrosive to copper wires and electronics. If the internal seals of the pump leak, the fluid contacts the control circuit board, shorting it out. Running the tank completely empty can also burn out the pump motor because the fluid acts as a cooling lubricant.

Frequently Asked Questions

Diesel exhaust fluid is 67.5 percent water and freezes at 12F. The heater prevents the fluid from freezing inside the pump and thaws it out when you start the engine on cold mornings.
Common signs include an engine warning countdown, a check engine light with codes for DEF pressure low (like P20E8), and a humming noise from the tank area when you turn the key.
No. The engine computer will drop the truck into a speed-restricted limp mode and eventually prevent starting if the DEF tank remains empty.
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