1. What is the DPR System?
In a diesel prime mover, the DPR system captures soot produced during combustion.
How it differs from DPF
While the terms are often used interchangeably, DPR specifically refers to Hino’s "Reduction" system, which often combines a Diesel Oxidation Catalyst (DOC) and the filter into one unit to more efficiently manage exhaust temperatures and chemical reactions.
2. The 3 Stages of Regeneration
Regeneration is the process of burning off the trapped soot by raising exhaust temperatures to approximately 500°C–600°C, converting the soot into a tiny amount of ash.
I. Automatic (Passive/Active) Regeneration
This happens while you are driving.
Passive: Occurs naturally when the engine is under high load (e.g., highway driving), and exhaust heat is high enough to burn soot without extra fuel.
Active: If the soot level reaches a certain threshold (usually around 40-50%), the engine computer (ECU) automatically injects a small amount of extra fuel into the exhaust stroke to artificially boost the temperature.
No driver action is needed.
II. Manual (Parked) Regeneration
If the truck is driven mostly in "stop-and-go" traffic, the exhaust never gets hot enough for automatic cleaning. A DPR warning light will begin to flash on your dashboard, signaling that you must perform a manual burn.
III. Forced Regeneration
If the manual regeneration is ignored and the soot level reaches a critical point (often indicated by a "Check Engine" light or a "Limp Mode" warning), the system locks the driver out. At this stage, a diagnostic scan tool (like Hino DX2/DX3) is required to force the system to clean itself.
3. Steps for Manual (Parked) Regeneration
When the DPR light flashes, follow these steps immediately to avoid a trip to the workshop:
Find a Safe Location: Park the vehicle in an open area.
The exhaust will become extremely hot. Ensure there are no flammable materials (dry grass, paper, fuel) near or under the exhaust pipe. Set the Vehicle:
Bring the engine to an idle.
Engage the Parking Brake.
Place the transmission in Neutral.
Check Prerequisites:
Ensure the engine is at operating temperature (the needle should be in the middle of the gauge).
Turn off the Air Conditioning and any Power Take-Off (PTO) switches.
Initiate the Burn: Press and hold the DPR/DPF Switch on the dashboard (usually for 2–3 seconds).
Monitor the Process:
The engine RPM will automatically rise (often to 1,200–1,500 RPM).
The DPR light will turn from flashing to solid.
Do not touch the pedals or move the gear lever, as this will cancel the process.
Completion: The process usually takes 15 to 30 minutes. Once finished, the engine will return to its normal idle speed, and the dashboard light will turn off.
Pro Tip: If your DPR light is flashing, try to complete the regeneration as soon as possible. If the soot level reaches "Level 4" or "Level 5," the filter may become so clogged that it requires a manual "bake" in an oven or a complete (and very expensive) replacement.