The diesel particulate filter (DPF) traps soot from diesel engines and, every so often, burns it off by raising the exhaust temperature. If you do lots of short journeys, that clean-out never gets to finish, the filter clogs up and the warning light comes on. At that point, a forced regeneration with a diagnostic tool can sort it out without taking anything apart.
Passive, active and forced regeneration
- Passive: happens on its own when you drive at a steady speed and the exhaust gets hot enough.
- Active: the engine control unit starts it by itself when it detects a loaded filter, by changing the injection. If you switch the engine off halfway, it is interrupted.
- Forced or service regeneration: you trigger it from the diagnostic tool, with the car stationary and following the conditions set by the manufacturer.
When forcing it makes sense
A forced regeneration is for a filter loaded with soot, not a cure-all. Before you start one, read the engine fault codes. If there are codes for the differential pressure sensor, exhaust temperature, EGR valve or injectors, fix that cause first: otherwise the filter will simply fill up again.
Nor does it deal with ash, the residue left after the soot burns, which builds up with mileage. A filter full of ash needs cleaning or replacing.
Safety: during regeneration the exhaust gets extremely hot. Do it outdoors or in a workshop with fume extraction, away from dry grass, paper or anything flammable, and don't touch the exhaust pipe or the filter area until they have cooled. Don't leave the car unattended while the process runs.
Forced regeneration step by step
- Check the oil level. Repeated failed regenerations can dilute fuel into the oil. If the level has gone up, change the oil first.
- Check the fuel. Many manufacturers require a minimum amount in the tank before the process will run; the tool usually tells you.
- Park somewhere safe and well ventilated, with the handbrake on and the gearbox in neutral or P.
- Connect the tool to the OBD2 port, identify the vehicle and read the engine faults. Note down the codes and freeze frame data before you clear anything.
- Start the engine and let it reach operating temperature. The tool will check the preconditions (coolant temperature, zero road speed, no blocking faults).
- Go into Service → DPF and choose regeneration. Some makes also offer other options, such as initialisation after a filter change or a relearn after replacing the control unit.
- Follow the on-screen instructions and wait. You will notice the revs rise and the cooling fan start. Don't touch the accelerator or switch the engine off unless the tool asks you to.
- When it finishes, leave the engine idling for a few minutes to settle, then read the faults again. If any codes from the process remain, clear them and check they don't come back.
- Take it for a road test at a steady speed to confirm the warning light doesn't come back on.
If the tool won't let you start a regeneration because the soot level is too high, don't keep trying: the manufacturer blocks the process to prevent damage. At that point the filter has to come off to be cleaned or replaced.
If you replace the filter or sensor
After fitting a new or cleaned DPF, the control unit still thinks the filter is loaded. That is what the DPF reset or initialisation function is for: it clears the learned values. Always run it after replacing the filter or the differential pressure sensor, if your car requires it.
Which iCarsoft tools regenerate the DPF
| Tool | Vehicles | Notes |
|---|---|---|
| CR Pro | Cars, 58 makes | DPF is one of its 9 service functions |
| CR Pro+ | Cars, multi-brand | Adds EGR, NOx sensor, AdBlue and bidirectional control |
| CR Max P | Cars, 58 makes | 50 functions, also includes GPF (petrol particulate filter) |
| V2.0 single-brand (for example, VAWS V2.0) | One make or group | The same 9 functions as the CR Pro |
| HD V4.0 | Trucks and heavy vehicles | DPF and SCR aftertreatment |
The V1.0 single-brand tools do not include the DPF function. If your diesel also has EGR or AdBlue, the CR Pro+ or the CR Max P let you deal with the whole exhaust system from one tool. For fleets and heavy vehicle workshops, see our truck diagnostic tools collection.
How to stop the DPF clogging again
- Every now and then, do a motorway run at a steady speed.
- If the warning light comes on, don't switch the engine off in the middle of an active regeneration.
- Use oil to the specification the manufacturer requires for engines with a particulate filter.
- Check for EGR, injector and sensor faults: an engine that burns poorly produces more soot.
If the warning light returns a few days after a regeneration, don't keep repeating the process. It is a sign that something in the engine or the exhaust system itself is failing, and fault diagnosis will help you find it before the filter is damaged.
