How to Force a DPF Regen on a Freightliner with Detroit DD15 (Step-by-Step)

How to Force a DPF Regen on a Freightliner with Detroit DD15 (Step-by-Step)

If your Detroit DD15 is showing high soot levels or derating due to an incomplete regen, a forced DPF regeneration may be the fastest way to clear the problem without a visit to the dealer. In this guide, we’ll show you how to safely run a forced regen on a Freightliner using dealer-level software like Detroit DDDL.

When Should You Perform a Forced Regen?

A forced regen is recommended when:

  • The truck is stuck in derate mode (5 MPH or 25% torque)

  • You see fault codes like SPN 3719 FMI 0 or SPN 3720 FMI 15

  • Soot level is > 80% and passive regen is not triggering

Tools Needed:

  • Diesel laptop with Detroit DDDL 8.x installed

  • RP1210 adapter (Nexiq USB-Link 2, Inline 7, or equivalent)

  • Good battery charge or running engine (do NOT allow regen to start with low voltage)

Step-by-Step: How to Force a Regen

✅ Step 1: Connect to the Truck

  • Plug your adapter into the 9-pin diagnostic port

  • Launch Detroit Diesel Diagnostic Link (DDDL)

  • Let it fully connect to the MCM, CPC, and ACM modules

✅ Step 2: Check Fault Codes First

  • Go to Faults tab

  • Clear any inactive faults

  • Note active codes related to DPF, DOC, SCR, or NOx sensors

✅ Step 3: Go to the Aftertreatment Tab

  • Select the ACM (Aftertreatment Control Module)

  • Choose "DPF Regen" from the available service routines

✅ Step 4: Begin the Regen

  • Click Start Regen

  • Confirm you’re in a safe, well-ventilated outdoor location

  • The regen process takes 20–45 minutes depending on soot load

✅ Step 5: Monitor the Process

Watch:

  • EGT sensors (Exhaust Gas Temperature) – they should reach 1000°F+

  • Soot level % – should decrease steadily

  • DOC and DPF inlet/outlet temps – to confirm burnoff

What to Do If the Regen Fails

Common reasons for a regen failure:

  • Faulty NOx or delta pressure sensor

  • Clogged DPF or DOC

  • DPF is too full to regen (replace required)

  • Engine not at required idle temp or RPM

Codes That Signal It's Time for a Regen

SPN Code Description Action
SPN 3719 Soot Load Above Threshold Regen immediately
SPN 3720 DPF Zone Too Full May require replacement
SPN 4094 Ash Accumulation Monitor for long-term cleaning
SPN 3563 NOx Sensor Failed Replace before regen

Wrap-Up:

A forced DPF regen can save a tow or dealer visit, but it must be done correctly to avoid damage. With the right tools and live data monitoring, most techs can complete a regen in under an hour and clear a 5 MPH derate.

Need the Software to Perform Regens?

Our diesel diagnostic laptop kits come pre-loaded with Detroit DDDL and plug-and-play tools to perform regens, reset soot levels, clear faults, and more — with no subscriptions required.
👉 Shop Now at NoFeeDiesel.com

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