Powertrain, generic (extended)

P20F5 Reductant Consumption Too High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P20F5 is set when more diesel exhaust fluid is used, or has to be corrected away, than the control unit planned. In VW's 2014 Touareg TDI data book the trigger is an SCR adaptation value of 0.51 or lower: the NOx feedback keeps cutting the commanded dose because more fluid evidently reaches the catalyst than intended. GM maps the same idea to P249E (factor below 0.41, Type B). Likely reasons are a dosing valve that drips or does not close fully, an external leak downstream of the pressure sensor that empties the tank faster, or a pressure sensor reading low so the pump overdelivers. Jeep lists P20F5 with P20F4 on the 2.2 L diesel Cherokee and cures both with dosing unit software (18-088-20). An Isuzu patent also aims at a valve that keeps spraying. Overdosing risks ammonia slip and deposits.

Likely causes

Dosing valve dripping or not sealing between pulses
External leak at the valve or its supply line
Pressure sensor reading low, causing excess delivery
Dosing control unit software requiring an update

Symptoms

  • Check engine light and DEF warning
  • DEF tank empties faster than usual, white crust around the dosing valve
  • Ammonia smell or deposits in the exhaust

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–1,200
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant injection valvereductant supply linereductant pressure control valve

Related codes

P20F4P249EP20F6P20E9P202E

References: static.nhtsa.gov, static.nhtsa.gov, gsi.ext.gm.com, patents.google.com.