Theory Of Operation

The Diesel Exhaust Fluid (DEF) Pressure Sensor is a three wire sensor, integrated into the DEF Supply Pump assembly and is not serviceable separate. The DEF Pressure Sensor monitors supply pressure to the DEF Injector. The Diesel Exhaust Fluid (DEF) Dosing Control Unit provides a 5-Volt Supply and a ground to the DEF Pressure Sensor. The sensor provides a signal to the DEF Dosing Control Unit on the DEF Pressure Sensor Signal circuit. This DEF Pressure Sensor Signal voltage changes, based on the diesel exhaust fluid pressure supplied by the DEF Supply Pump. The DEF Dosing Control Unit will detect a low signal voltage at low diesel exhaust fluid pressures, and a high signal voltage at high diesel exhaust fluid pressures. The DEF Dosing Control Module will illuminate the MIL light via the Powertrain Control Module (PCM) immediately after the diagnostics runs and fails. Diesel exhaust fluid injection into the aftertreatment system is disabled. The DEF Dosing Control Module will turn off the MIL light via the PCM when the monitor runs and passes in three consecutive key cycles.

The first warning will occur when the p-code becomes pending or active. The customer will hear a chime and get an EVIC message reading "Service DEF System See Dealer." The second warning level will occur if the customer continues to drive and the code has not cleared. The customer will hear a chime and get an EVIC message reading "Speed Limited to 5 mph in XXX MILES See Dealer". Upon driving until the countdown reaches zero, the customer will hear a chime and get an EVIC message reading "5 mph Max on Restart, Long Idle or Refuel See Dealer." Upon key-off, refuel, or 1 hour long idle, the EVIC message will read, "Speed Limited to 5 mph See Dealer." Once induced to a 5 mph derate, the inducement will not clear unless the diagnostic runs and passes, or the PCM is recalibrated.