P20F5Reductant Consumption Too High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyDosing valve dripping or not sealing between pulses
- PossibleExternal leak at the valve or its supply line
- RarePressure sensor reading low, causing excess delivery
- RareDosing control unit software requiring an update
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €0 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.