P2002 – DPF Efficiency Below Threshold (CDI)
On Mercedes CDI diesels, P2002 is often tied to regen inhibition or differential pressure sensor drift — not always a “dead DPF”.
How it usually shows up
- Reduced power / torque limiting under load
- DPF light or emissions warning
- Historic-only code after interrupted regen
Most common causes (Mercedes)
- Regen inhibited by low voltage, temp control or prior faults
- EGR flow issues causing secondary DPF efficiency flags
- Differential pressure sensor drift or blocked hoses
- True DPF restriction (soot/ash)
Practical test plan
- Check if the fault is active vs historic (pending + current matters).
- Verify battery/charging stability; low voltage can inhibit regen.
- Compare DPF differential pressure at idle and under load (watch for implausible spikes).
- Check pressure sensor hoses for blockage/condensation.
- If EGR flow faults exist, resolve them first and re-test.
- Only consider DPF replacement after confirming genuine restriction and failed regen attempts.
Related reading
CDI DPF & EGR Behaviour
Mercedes CDI regen inhibitors and recurrence logic.
P2463
DPF soot accumulation – why faults return.
P0401
EGR flow insufficient – common causes and tests.
Tip: If you have multiple codes, start with the one that appeared first, then confirm with live data before replacing parts.