Mitsubishi Triton: DPF Blockage from Incomplete Regeneration & Fuel Dilution

The 4N15 uses post-injection of diesel fuel to raise exhaust temperatures during DPF active regeneration. Short urban trips repeatedly interrupt regeneration cycles before completion. Unburned post-injection fuel washes past piston rings into the sump, diluting engine oil with diesel. The ECU tracks an oil dilution value and can enter limp mode or demand early oil changes. Severely blocked DPFs require forced regeneration or replacement. The linked oil dilution damage can accelerate bearing and ring wear if not managed via mandatory ECU oil dilution counter resets after every oil change.

• DPF warning light or engine management light with fault codes related to exhaust pressure or particulate load
• Diesel smell from engine oil dipstick indicating fuel dilution
• Oil level appearing higher than expected between service intervals
• Vehicle entering limp mode with fault code P252F (excessive fuel dilution)
• Loss of power under load, particularly on highway at high speed

1. 1

   Check oil level and smell dipstick for diesel odour, which indicates fuel dilution.

2. 2

   Check DPF differential pressure sensor live data for elevated soot load readings.

3. 3

   Review service records for history of DPF regeneration or replacement.

4. 4

   If a workshop inspection is possible: Connect a compatible scan tool and read live oil dilution percentage value from ECU (P252F fault code may be present).

Parts involved: Diesel particulate filter.

$400 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the vehicle been used mainly for short city trips or does it regularly do highway runs over 30 minutes?”
• “Has the DPF warning light ever illuminated, and has forced regeneration or DPF replacement been required?”
• “Has the ECU oil dilution counter been reset with a scan tool after every oil change?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.