Hope some one can help. I received a P21B0 code and replaced the DEF tank Reservoir. After one day I received just the P20E8 code, low reductant pressure. I am not sure that the Pump is really bad, no other codes come up. I want to make sure my install of the reservoir seal is not the cause of the low pressure. When I installed the reservoir, I installed the reservoir seal down from the tank top and over the outside lip of the reservoir. I could not remember if the seal was placed around the outside lip or just dropped down from the tank top and laid on the inside of the reservoir. Anyone know if the seal should be placed on the inside or the outside of the reservoir lip inside the tank. This may be the cause of my new code, low pressure?