OperationAfter the key is turned OFF on a vehicle with SCR system, apumping sound may be heard from underneath the vehicle. Thesound is made by the Aftertreatment DEF dosing unit while itpurges any unused DEF from the system and returns it to theDEF tank. This is normal system operation. It takes about 70seconds to complete.CAUTIONTo prevent vehicle / property damage, afterturning the key OFF on a vehicle with SelectiveCatalyst Reduction (SCR) system, do notdisconnect the vehicle batteries while youcan hear a pumping sound from underneaththe vehicle. The sound may last for about 60seconds.Low DEF LevelWARNINGTo prevent property damage, personal injury, and/ or death, maintain the adequate Diesel ExhaustFluid (DEF) level to avoid a loss of engine powerand vehicle speed.On the instrument panel, you can monitor the fluid level using theDEF Level Gauge. You will see additional warnings if the DEFis too low. If DEF level decreases to 2.2% or lower, the engineperformance will start to be derated by at least 25%; if the DEFlevel remains 0% for an extended time, the vehicle speed willbe limited to 5 mph (8 km/h). Refill the DEF tank with approvedDEF at any point, and the vehicle will resume normal operation.See the following table for a detailed explanation of indicatorsabout low DEF level.168
