DEF Pump Unable to Build Pressure After Replacement

After replacing the Diesel Exhaust Fluid (DEF) pump (Fig. 9) on some 2017-2020 Colorado, Cruze, Express, Silverado 1500, Silverado 2500/3500, Canyon, Sierra 1500, Sierra 2500/3500; 2017-2019 Savana; 2018-2019 Equinox, Terrain; and 2019-2020 Silverado 4500/5500/6500 models equipped with the 2.8L diesel engine (RPO LWN), 1.6L diesel engine (RPO LH7), 3.0L diesel engine (RPO LM2), or 6.6L diesel engine (RPO L5P, L5D), the pump may not build pressure. DTCs P20E8 (Reductant Low Pressure) and P249C (Excessive Time To Enter Closed Loop Reductant Injection Control) may be set.

Fig. 9

Under typical operation, the electrically-operated DEF (emissions reductant) pump within the DEF reservoir supplies pressurized reductant to the reductant injector located upstream of the Selective Catalyst Reduction. A reductant level sensor within the reductant reservoir provides the reductant control module a signal indicating reductant level. The reductant pressure sensor provides the reductant control module with a voltage signal proportional to the reductant pressure generated by the reductant pump. The reductant control module varies the duty-cycle of the pump voltage to maintain reductant pressure within a calibrated range.

 

Leak Test

After replacing the DEF pump and confirming that the system is unable to build pressure, inspect for any leaks, loose connections or kinks in the supply line.

Also perform an initial leak test three times using a scan tool. If low pressure is present, the DEF pump filter may have dried out.

 

Saturate the Pump Filter

Allow the vehicle to sit overnight with the new pump and DEF fluid in order to re-saturate the DEF pump filter. In the morning, perform the leak test three additional times. The pump should now be able to build pressure.

For additional information, refer to Bulletin #20-NA-110.

– Thanks to Larry Yaw