If a 6.7 won't complete an active regen, ~70% of the time the DPF itself is fine. The other component upstream is what's broken.
Most common causes (in order)
- EGT sensor giving wrong reading. The PCM thinks the DPF temp didn't reach target — actually it did. New sensor, regen completes.
- Exhaust pressure sensor / DPF differential pressure sensor faulted. Same idea — sensor lies, PCM aborts.
- DEF system fault. The truck won't run a regen if it can't dose DEF correctly.
- Fuel doser injector clogged. The 6.7 sprays fuel post-combustion to heat the DPF; a clogged doser means no heat.
- Actually clogged DPF. Last resort.
We always check 1–4 before we suggest 5. Saves the customer real money.