P2002 — Diesel Particulate Filter Efficiency Below Threshold

What Is P2002?

P2002 is stored on diesel vehicles when the ECU detects that the diesel particulate filter (DPF) has become blocked to the point where it can no longer clean itself efficiently. The DPF traps soot from exhaust gases, periodically burning it off through a process called regeneration. When soot loading exceeds the threshold and regeneration repeatedly fails, P2002 is stored and the car will usually enter limp mode. Ignored long enough, the DPF will need replacing — a very expensive job.

Common Symptoms

Engine management light on
Possible limp mode (restricted to 2,000–2,500 rpm)
DPF warning light (on cars that have one)
Increased fuel consumption (the ECU injects extra fuel to raise exhaust temperatures for regen)
Excessive diesel smell
Black smoke under acceleration

Common Causes

Insufficient Motorway Driving DPF regeneration requires sustained high exhaust temperatures (typically above 500°C). Short journeys prevent this.

Low Fuel Level During Regen The ECU will not attempt a regen below a quarter of a tank. Habitually running low prevents regeneration.

EGR Fault A faulty EGR system affects exhaust temperatures and can prevent successful regen.

DPF Pressure Sensor Fault The differential pressure sensor monitors DPF soot loading. A faulty sensor gives incorrect readings.

Faulty Glow Plugs Poor combustion quality affects soot loading and regen temperatures.

Engine Oil Level Too High Excess oil burns through the DPF and rapidly loads it with ash.

Biodiesel or Poor Quality Fuel Causes excessive soot loading and deposits that the DPF cannot burn off.

How to Diagnose P2002

Check DPF Soot Loading

Connect OBD scanner and check DPF soot loading percentage. Under 80% is healthy. Over 100% means regen has failed repeatedly.

Attempt Active Regeneration

With a professional scan tool, force an active regen whilst the engine is at operating temperature. This burns off accumulated soot.

Check for Companion Codes

EGR faults, DPF pressure sensor codes, and fuel system codes will all prevent successful regen.

Check Engine Oil Level

If over the max mark, change the oil immediately. Excess oil enters the DPF via blow-by.

Inspect DPF Pressure Sensor

Check DPF pressure sensor and pipes for damage, cracks or blockages.

Fuel and Oil Critical Never attempt a DPF regen on a car that is low on fuel or engine oil. The regen process uses both, and running out mid-regen can cause significant engine damage.

DPF is Mandatory A DPF is a legal requirement on all diesel cars registered after 2009. Removing it is illegal for road use and will cause an automatic MOT failure. Do not be tempted by DPF delete services.

Verdict

P2002 is serious but not always terminal for the DPF. Catch it early, attempt an active regen, fix any underlying faults, and change your driving habits. Left too long, the DPF will need replacement at significant cost.

Frequently Asked Questions

You can attempt a passive regen by driving at motorway speeds (60–70 mph) for 20–30 minutes with the engine fully warm. This works if soot loading is under around 80%.

Expect 500–1,500 pounds for the part alone. Labour adds significantly. Some specialist companies offer DPF cleaning as an alternative for 150–300 pounds.

Professional ultrasonic cleaning works well on DPFs that are heavily soot-loaded but not ash-blocked or damaged. It won't work on cracked or physically damaged filters.

Yes. If most of your driving is under 10 miles, the DPF may never reach regen temperature. Occasional longer drives are essential for diesel vehicles.

It depends on which warning light the code is triggering. Since 2018, any car presenting with an illuminated amber Engine Management Light (EML) at the MOT is a Major failure under DVSA rules — even if the car drives perfectly. A red warning light is always a Major or Dangerous failure depending on context. If clearing the fault makes the light go out and the code does not reappear during the pre-test drive, you will pass; if the code returns within minutes of clearing, the underlying fault must be fixed before MOT day. A tester is required to fail the car on the light being on, regardless of whether the underlying fault is something safety-critical or not. For codes that affect emissions specifically (catalyst, lambda, EGR), the car may also fail the actual emissions check. Fix the cause, clear the code, and drive the car for a few miles before the test.

P2002 — Diesel Particulate Filter Efficiency Low