Particulate Trap Efficiency Below Threshold (Bank 2)

Possible causes

• CommonMostly short journeys, so regeneration never completes
• CommonRegeneration repeatedly interrupted by switching the engine off part way through
• CommonFaulty pressure or temperature sensor around the filter
• CommonFilter genuinely full or damaged
• CommonEngine fault producing excess soot - injectors, EGR, turbo
• PossibleWrong engine oil - some oils leave ash that permanently blocks the filter

What you might notice

• Check engine light or particulate filter warning
• Reduced power or limp mode
• Worse fuel economy
• Cooling fan running more than usual
• Smell of hot exhaust after a run

What to check, in order

1. Look at how the car is used. If it does mainly short trips, that is very likely the cause, and a sustained run at motorway speed for twenty minutes or so often lets a regeneration complete.
2. Never switch the engine off during an active regeneration if you can avoid it. Interrupting it repeatedly is how a filter goes from full to blocked.
3. Read all codes. Sensor codes alongside this one usually name the real fault, and sensors are far cheaper than filters.
4. Check what engine oil is being used. Low-ash oil is specified for these engines for a reason - ordinary oil leaves deposits the filter cannot burn off.
5. Look for an engine fault producing excess soot. A filter blocked by a leaking injector will block again after cleaning unless the injector is fixed.