Modern diesel trucks use several dashboard lights and symbols to warn you about soot buildup, regeneration problems, and DPF filter issues. Understanding what each regen light means can help you avoid unnecessary breakdowns, failed regenerations, and the dreaded 5 MPH derate.
This guide explains every common diesel regeneration light found on Cummins, Detroit, CAT, Paccar, Volvo, International, and pickup trucks like Ford, GM, and Ram.
Common Diesel Regeneration & DPF Warning Lights
Although symbols vary by manufacturer, the meanings are almost always the same across all diesel engines.
1. DPF Light (Diesel Particulate Filter Icon)
This is the most common regen-related dashboard light. It looks like a filter with small dots inside.
Meaning: The DPF is becoming full of soot and needs regeneration soon.
What to do:
- Drive at highway speeds to allow passive regen
- If light stays on → perform a parked regen
- If it flashes → immediate attention is required
2. Regen Light / Exhaust Temperature Light
Often shows an exhaust pipe with heat waves.
Meaning: The truck is actively regenerating, and exhaust temperatures are high.
What to do:
- Continue driving normally
- Do not shut off the engine
- Do not idle for long periods during regen
3. Parked Regen Required Light
This symbol usually shows a DPF with an arrow pointing downward or a message on screen.
Meaning: The truck needs a parked regeneration because soot levels are too high.
What to do:
- Park safely
- Apply parking brake
- Initiate parked regen from the dash
If the parked regen fails, diagnostic software is required.
4. Check Engine Light (Aftertreatment Related)
When the check engine light appears with emissions faults, it often relates to:
- DPF pressure sensor
- EGR valve or cooler
- NOx sensor
- Temperature sensor
- DEF system problems
This light can prevent regeneration from starting.
5. DEF Light / SCR Warning Light
Indicates the DEF system has a problem or DEF quality is bad.
If ignored: This will eventually cause regen failure and SCR derate.
6. 5 MPH Derate / Engine Derate Light
When regenerations fail repeatedly, the truck may enter the severe emissions derate.
Meaning: The engine will limit power and top speed to prevent damage.
You must:
- Fix underlying faults
- Perform forced regen using diagnostics
What to Do When the DPF Light Flashes
A flashing DPF light means the filter is almost completely full. This is urgent.
Steps:
- Perform a parked regen immediately
- If it fails → do not continue driving
- Use diagnostic laptop to run forced regen
Continuing to drive can trigger a shutdown.
Why Regeneration Lights Turn On
Common causes include:
- Low exhaust temperatures
- Short-trip driving
- High soot buildup
- EGR system problems
- DEF dosing issues
- Failed NOx or temp sensors
Many dash warnings mean the DPF can no longer regenerate normally.
How to Clear Regen Warning Lights
The most reliable way is by using a diagnostic laptop.
With software like Diesel Tech, Universal Diag, INSITE, DDDL, CAT ET, or ESA, you can:
- Read exact fault codes
- Check soot load and DPF pressure
- Run forced regeneration
- Reset aftertreatment system
- Verify sensor readings
When You Should NOT Ignore Regen Lights
- DPF light flashing
- Parked regen requested repeatedly
- Regen fails to complete
- Soot levels staying high after regen
- Truck entering derate mode
Ignoring these signs can lead to major damage or a roadside shutdown.
How to Prevent Regen Warning Lights
- Avoid long-term idling
- Drive at highway speeds regularly
- Use high-quality DEF
- Fix NOx or EGR issues early
- Perform DPF cleaning at proper intervals
- Monitor soot levels with diagnostics
Need Help?
If you’re unsure what your regen light means or need help diagnosing the aftertreatment system, contact us below:
- Phone (Toll Free): (877) 210-3245
- Email: info@truckscanners.com
- Contact Page: https://truckscanners.com/contact/
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Need a diagnostic laptop that clears regen lights, runs forced regens, and diagnoses DPF/DEF/EGR problems? View our fully-loaded kits below:
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