If you work with diesel ECUs, you will deal with DPF. Here’s what’s actually happening inside the ECU during a regen.
Step 1: Soot load estimation
The ECU doesn’t directly measure soot. It calculates it using the differential pressure sensor + an internal model that accounts for engine load, fuel quantity, exhaust temperature, and driving profile.
Step 2: Conditions check
Before a regen can start, the ECU checks: Is the car moving? Is coolant temperature above minimum? Is battery voltage adequate?
Step 3: Raising exhaust temperature
The DPF needs ~600°C+ for active regen. The ECU achieves this by:
- Retarding injection timing
- Opening the EGR
- Post injection (the critical one for DPF-out temperature)
- Throttle intervention
Step 4: Active regen execution
The ECU holds elevated temperature until calculated soot load drops below threshold.
Why this matters for calibration
If you’re doing a Stage 1 on a DPF-equipped car and you only touch rail pressure, SOI, and quantity — you haven’t considered what happens when regen triggers under your new fueling strategy.
And if you’re doing a DPF-off job without understanding this chain — you’re guessing, not calibrating.
This is covered in detail in Diesel Practice, the DPF/EGR section.