EPA10 Diesel Exhaust Fluid (DEF) Purge Cycle

For EPA10 only, the DEF purge cycle is used to protect the DEF system from freezing. The purge cycle starts right after the key is shut off. The vehicle's air system is used to evacuate excess DEF from the DEF metering unit and nozzle supply hose. During the purge cycle, air can be heard leaking, which should not be mistaken as a leak. It is normal for the air pressure gauge to drop 9 to 12 psi during this routine with the engine off.