Tech Tip: Resolving a Lack of Pressure in the Def Pump
Vehicle Involved:  2016–2020 Chevrolet Colorado; 2018–2019 Chevrolet Cruze; 2017–2020 Chevrolet Express; 2018–2019 Chevrolet Equinox; 2020 Chevrolet Silverado 1500; 2017–2019 Chevrolet Silverado 2500/3500 HD and 2019–2020 Chevrolet Silverado 4500/5500/6500 HD; 2016–2020 GMC Canyon; 2017–2020 GMC Savana; 2019–2020 GMC Sierra 1500; 2017–2020 GMC Sierra 2500/3500; 2019 GMC Sierra Limited; and 2018–2019 GMC Terrain models equipped with either the 2.8L (RPO LWN), the 1.6L (RPO LH7), the 3.0L (RPO LM2) or the 6.6L (RPO L5P, L5D) diesel engines.

After replacing the Diesel Exhaust Fluid (DEF) pump on one of the above vehicles, technicians may find that the pump is not building sufficient pressure for proper operation. In addition, DTC P20E8 (Reductant Low Pressure) and P249C (Excessive Time to Enter Closed Loop Reductant Injection Control) may be set. The electrically operated DEF (emissions reductant) pump, which is located within the DEF reservoir, is designed to deliver pressurized reductant to the reductant injector located upstream of the Selective Catalytic Reduction Catalyst.

A sensor within the reductant reservoir sends the reductant control module a signal indicating existing reductant level. The reductant pressure sensor provides the module with a voltage signal proportional to the reductant pressure generated by the pump. The module varies the duty cycle of the pump voltage to maintain pressure within a calibrated range.

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.

To help resolve the issue, allow the DEF pump to sit in DEF fluid overnight in order to re-saturate the filter. The following morning, perform the leak test three additional times. The pump should now be able to build pressure.

Important: Be sure to perform the leak test three times before considering a pump replacement.

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