Freightliner DPF Regen Required — How to Fix

What Does This Error Mean?

A DPF regen required indicator means the diesel particulate filter is full of soot and needs to burn off. Drive at highway speed for 30+ minutes for a passive regen, or perform a manual stationary regen if needed.

Affected Models

Freightliner Cascadia
Freightliner Cascadia Evolution
Freightliner M2
Freightliner Coronado
Freightliner 122SD

Common Causes

Excessive low-load operation preventing passive regen
Frequent short trips not allowing engine to reach regen temperature
Failed DOC (diesel oxidation catalyst) or DPF damage
Failed soot or pressure sensor
Stuck EGR valve causing excessive soot

How to Fix It

Drive at highway speed for 30 minutes.

Most regens happen automatically when the engine is at high temperature for sustained periods. Drive at 55+ mph for 30 minutes and the regen often completes without driver intervention.
Initiate a manual stationary regen.

Park in a safe area away from flammable materials. On Freightliner Cascadia, hold the regen switch on the dash for several seconds. The engine RPM will rise and exhaust temperatures will increase. The HEST (High Exhaust System Temperature) light will illuminate during regen.
Allow regen to complete.

Stationary regen typically takes 30–60 minutes. Do not interrupt — leaving regen incomplete worsens the soot loading. The system will indicate when regen finishes.
Check sensors if regen does not complete.

If manual regen will not start or fails to complete, the differential pressure sensor or temperature sensors may be faulty. A Detroit Diesel scan tool (DDDL) reads sensor data and identifies the issue.

When to Call a Professional

If manual regen does not complete, a Detroit Diesel technician can perform a forced regen with diagnostic tools or replace damaged aftertreatment components.