DEF FLUID HEATER
2012 - 2016 LML / LGH
Silverado and Sierra
(includes tank nut, tank seal and hardware kit)
Commonly called the "DEF Heater", the diesel exhaust fluid heater is located in the DEF (Diesel Exhaust Fluid / Urea) tank and actually contains the pickup tube for the reductant pump module, an electric heating element, a temperature sensor, a pressure sensor, and an electrode-type level sensor. GM terms the whole unit the "reservoir kit, emission reduction fluid tank".
Due to EPA requirements, faults in the DEF system which cause codes to set may cause the vehicle to operate in derate mode limiting engine power and speed.
Following is a brief description of the functions of this component:
The on-board DEF reservoir holds approximately 19 liters (5 gallons) of
DEF - also known as reductant. An ECM controlled pump within the
reservoir supplies pressurized reductant to the DEF injector located
upstream of the SCR. A smart DEF level sensor within the reductant
reservoir sends the ECM a serial data message indicating reductant
level. The DEF pressure sensor provides the ECM with a voltage signal
proportional to the reductant pressure generated by the DEF pump. The
ECM varies the duty-cycle of the pump voltage to maintain reductant
pressure within a calibrated range.
The state of the reductant purge valve determines whether the exhaust
fluid from the reductant pump is directed to the reductant injector or
returned to the reservoir. In the normally de-energized state, the
reductant purge valve directs reductant from the pump to the reductant
injector. When the ignition is turned OFF, the ECM energizes both the
reductant purge valve and reductant pump for about 30 to 45 seconds in
order to purge the supply line of reductant. The ECM also commands the
reductant injector to 100 percent to prevent vacuum from forming during
the purge process. Purging prevents the reductant from freezing in the
pump or supply line to the reductant injector.
The ECM energizes the reductant injector to dispense a precise amount of
reductant upstream of the SCR in response to changes in exhaust NOx
levels. Feedback from NOx sensors 1 and 2 allow the ECM to accurately
control the amount of reductant supplied to the SCR.
There are 3 reductant heaters, one heater in the reductant reservoir,
one heater at the reductant pump, and one heater in the supply line to
the reductant injector as reductant will freeze at temperatures below
0°C (32°F). The ECM monitors the reductant temperature sensor located
within the reservoir in order to determine if reductant temperature is
below its freeze point. If the ECM determines that the reductant may be
frozen, it signals the Glow Plug Control Module (GPCM) to energize the
Reductant pump operation is disabled for a calibrated amount of time to
allow the heaters time to thaw the frozen reductant. Once the thaw
period expires, the ECM energizes the reductant pump to circulate warm
reductant through the de-energized reductant purge valve and back to the
reservoir. This is done to speed thawing. The ECM looks for an increase
in the reductant temperature to verify that the reductant reservoir
heater is working
Before replacing the DEF / urea heater / reservoir assembly for a related code, please be sure to follow factory diagnostic procedures, paying special attention to the integrity of wiring and connectors to avoid unnecessary part replacement.
Replaces the following part numbers (and others):
84412924, 22872118, 22902620, 23379348, F01C600337