Detroit Diesel engines (DD13, DD15, DD16) are known for strong performance, but they also rely heavily on a properly functioning aftertreatment system. If your Detroit truck is struggling to regenerate, constantly requesting parked regens, or entering derate mode, this guide explains the most common causes — and how to fix them.
This article covers all regeneration issues on EPA07, EPA10, GHG14, GHG17 Detroit engines.
How Detroit Diesel Regeneration Works
Detroit uses a Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), and Selective Catalytic Reduction (SCR) system. During regeneration, the engine raises exhaust temps to burn soot out of the DPF.
There are three types of regen:
- Passive Regen – Happens automatically while driving at highway speeds.
- Active Regen – ECM injects additional fuel to heat the DPF.
- Parked Regen – Driver must initiate from the dash.
If any part of the system fails, regeneration may not start or may fail repeatedly.
Most Common Detroit Diesel Regen Problems
1. High Soot Levels (SPN 3719)
This is the most common DPF-related fault on Detroit engines. It means soot has accumulated faster than regeneration can remove it.
Causes:
- EGR system problems
- Clogged DOC/DPF
- Short-trip driving
- Restricted turbo or low boost
Fix: Perform forced regen using DDDL. If soot level remains high, inspect EGR system and check DPF restriction.
2. Emissions Derate Active (SPN 5246)
This code activates after failed or incomplete regens.
Common triggers:
- Multiple failed regens
- DEF not dosing correctly
- NOx sensors out of range
- Soot level too high to continue driving
Fix: Perform forced regen. If derate returns, test NOx sensors and DEF system.
3. NOx Sensor Problems (SPN 4364)
These sensors are known failure points on DD engines. A bad NOx sensor prevents proper SCR operation, increasing soot and triggering frequent regens.
Fix: Replace failed NOx sensor and reset the SCR system using DDDL.
4. DEF System Issues (Doser, Pump, Quality Sensor)
Detroit’s DEF system includes:
- DEF pump
- Doser injector
- DEF quality sensor
- DEF filter
Any failure restricts proper emissions operation and increases soot.
Fix: Run SCR efficiency test in DDDL and check DEF pressure, line heat status, and doser operation.
5. Clogged DPF or DOC
If ash accumulation is too high, regeneration will not clean the filter.
Fix: Remove DPF for professional cleaning. Inspect DOC for face plugging.
6. Exhaust Temperature Sensor Failure
Detroit uses multiple temperature sensors (DOC Inlet/Outlet, DPF Inlet/Outlet). A bad temp sensor causes regen to fail immediately or never start.
Fix: Replace faulty sensor and clear codes.
7. EGR Valve & EGR Cooler Problems
Detroit engines are sensitive to EGR flow. A restricted EGR cooler or stuck EGR valve is a guaranteed way to overload the DPF.
Signs:
- Frequent regens
- Black smoke
- Poor idle
Fix: Test EGR components using DDDL. Clean or replace parts as needed.
How to Perform a Forced Regen on Detroit Diesel (DDDL)
Step 1: Connect to the Truck
- Use Nexiq USB-Link 3 (recommended)
- Turn key ON, engine OFF
- Open Detroit Diesel Diagnostic Link (DDDL)
Step 2: Check Aftertreatment Codes
Look for SPN/FMI codes affecting regen:
- SPN 3719 – Soot level high
- SPN 5246 – Emissions derate active
- SPN 4364 – NOx sensor fault
- SPN 3216 – DEF quality sensor
- SPN 3361 – DEF doser issues
Step 3: Start the Regen
- Navigate to Aftertreatment → DPF Service → Parked/Forced Regen
- Follow on-screen prompts
- Monitor temperatures (900–1200°F normal)
Step 4: Confirm Completion
- Soot level drops into normal range
- No active regen-related codes
- DPF pressure normal at idle
When Forced Regen Will NOT Help
Regen will not solve issues caused by:
- Failed NOx sensors
- DEF pump or doser failure
- Severely clogged DPF (full of ash)
- Boost leaks or turbo problems
- EGR cooler blockage
These require diagnostics and part replacement.
How to Prevent Detroit Diesel Regen Problems
- Fix EGR and NOx faults immediately
- Use high-quality DEF
- Minimize idling
- Perform regular DPF cleanings
- Monitor soot levels and regen history using DDDL
Need Help?
If your Detroit engine won’t regen, keeps entering derate, or you need help diagnosing SPN/FMI fault codes, contact us below:
- Phone (Toll Free): (877) 210-3245
- Email: info@truckscanners.com
- Contact Page: https://truckscanners.com/contact/
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