Disclaimer:
This post is based on my personal experience and intended for informational and educational purposes only. Procedures, tools, and parts may vary depending on the vehicle and situation. Always consult your service manual or a professional before performing any maintenance.For more information, please read the full disclaimer here.
No DPF Regeneration After Interrupted Cycle
A few days ago, my car started a DPF regeneration just as I parked in the garage. Unfortunately, I had to interrupt it. I already wrote about that here: DPF Regeneration Interrupted.
Today, I wanted to give it another chance.
What is Needed for Regeneration?
The car needs the right conditions before regeneration starts.
- Engine at normal operating temperature.
- Steady driving, usually on the highway.
- No errors in the system.
How Much Soot Mass is Needed?
Every car has thresholds.
For my BMW, regeneration usually starts when soot mass goes above ~24–28 g.
My Attempt on the Highway
I connected my diagnostic tool and recorded dozens of parameters. Later, I checked them in detail.
- Drive: 70 km on the highway (49 minutes), 10 km city driving.
- Engine RPM: Between 2,000 and 3,000 most of the time.
Parameters at the Start:
- Regeneration Release: Off
- Engine Operation Since Last Regeneration: 4:58:34
- Soot Mass: 24.41 g
- Kilometers: 118,984
- Exhaust Gas Differential Pressure: 4 hPa
Parameters at the End:
- Regeneration Release: Off
- Engine Operation Since Last Regeneration: 5:47:08
- Soot Mass: 30.75 g
- Kilometers: 119,065
- Exhaust Gas Differential Pressure: 5 hPa
Real Data Collected with Launch Diagnostc
Driving speed: 131 km/h
- Solid highway speed. DPF regenerations usually need sustained highway driving, and 130 km/h is generally sufficient.
- So the speed itself is not the limiting factor here.
Engine Speed: 2973 rpm
- This is a moderately high engine load, which is good because higher RPM helps reach exhaust temperatures needed for regeneration.
- Ideal DPF regeneration often occurs between ~2,000–3,500 rpm depending on engine load, so this is within the expected range.
Oil Temperature: 94 °C
- Engine temperature is normal.
- DPF regeneration usually requires the engine to be at normal operating temperature (around 90–105 °C), so this is okay.
DPF Soot Mass: 28.60 g
- This is approaching or slightly above typical trigger thresholds for passive or active regeneration (usually ~24–30 g for BMW diesels).
- So the soot mass is high enough that the ECU might normally consider starting regeneration.
DPF Exhaust Gas Differential Pressure: 51.96 hPa
- This value is higher than normal idle or clean filter pressure.
- Elevated differential pressure indicates some backpressure in the DPF, which usually triggers active regeneration.
- For BMWs, anything above ~50 hPa can indicate the filter is loaded, but the ECU might still wait for longer sustained driving or slightly higher soot mass. More information about DPF Exhaust Gas Differential Pressure you find here.
- In short: Under load (hills, acceleration): 30 – 70+ hPa -> Higher pressure due to exhaust flow
Conclusion
I will continue to learn and monitor parameters for ongoing regenerations. The highway run did not trigger regeneration. The soot mass kept rising instead. Should I worry?
All the conditions during my drive—speed, RPM, and oil temperature—were generally favorable for DPF regeneration. The soot mass was close to the typical threshold, and the exhaust gas differential pressure was elevated.
Despite this, regeneration did not start. This suggests that the ECU may still require one or more of the following:
- Slightly higher soot mass (e.g., above 30 g)
- Longer sustained highway driving
- Optimal combination of load, temperature, and duration
In short, nothing was “wrong” with the drive itself. My BMW is simply waiting for the precise conditions it considers safe to start regeneration.
