Faulty Emission Reduction Fluid Tank Heater

The Emission Reduction Fluid Tank heater may be faulty on some 2020 Silverado 1500, Silverado 2500HD/3500HD, Sierra 1500, Sierra 2500HD/3500HD; 2021 Tahoe, Suburban, Yukon and Escalade models equipped with the 6.6L Duramax diesel engine (RPO L5P) or 3.0L Duramax diesel engine (RPO LM2). If the Emission Reduction Fluid Tank heater is not operating properly, there may be a Service Emission System/Service Exhaust Fluid System message on the Driver Information Center along with an illuminated Check Engine MIL. DTCs P20BB (Reductant Heater 1 Control Circuit Low Voltage) and P20C3 (Reductant Heater 3 Control Circuit Low Voltage Test Status) also may be set in the Engine Control Module (ECM).

The faulty Emission Reduction Fluid Tank heater may be caused by the tank heating elements being exposed to Diesel Exhaust Fluid (DEF) and shorting to the pump ground. Within the Emission Reduction Fluid Tank is the Emission Reductant Fluid Supply Pump Module, which contains an electrically operating reductant pump; reductant level, quality, and temperature sensors; and reductant system heaters. (Fig. 16) The reductant control module is mounted outside the tank.


Fig. 16


To determine if there is a short to ground, measure resistance at the Emission Reductant Fluid Supply Pump Module (Fig. 17), which would indicate that the heater has been exposed to DEF.


Fig. 17


TIP: Be sure that the DEF tank is at least half full of DEF before performing the resistance measurement.

With the Emission Reduction Fluid Tank wiring harness disconnected, measure resistance from pin 9 to pin 14 using a Digital Multimeter. Next, measure resistance from pin 10 to pin 14. The illustration (Fig. 18) shows pin 9 (#1), pin 10 (#2), and pin 14 (#3).


Fig. 18


If either resistance reading is less than 10M ohm, the heater is faulty and the Emission Reduction Fluid Tank should be replaced. If both resistance readings are greater than 10M ohm, continue with diagnostics according to the appropriate Service Information.


Cold Weather Operation

The two reductant (DEF) heaters are designed to thaw DEF that has become frozen in temperatures below 32°F (0°C) in the Emission Reduction Fluid Tank and supply line to the DEF injector. The reductant control module monitors the reductant temperature sensor located within the Emission Reduction Fluid Tank in order to determine if reductant temperature is below its freeze point. If the control module determines that the reductant may be frozen, it energizes the reductant heaters. Reductant pump operation is disabled for a calibrated amount of time to allow the heaters time to thaw the frozen DEF.

For more information, refer to Bulletin #21-NA-002.


– Thanks to Larry Yaw

Escalade OLED Infotainment System Demo Mode
Auxiliary Transmission Oil Cooler Eliminated


  1. 2021 same issues with Def tank

  2. joseph wulffen says:

    I have seen 2 that have had the harness for the def module to pump corroded from water intrusion.
    its a bad design! you have all that sitting at the bottom of the tank covered with a shield to hold water in!!!

  3. replace def pump or tank assembly ?

  4. just got done replacing all the previous versions again new trucks?

Leave a Reply

Your email address will not be published.