Like all new diesel cars manufactured since 2008, BMW vehicles are equipped with Diesel Particulate Filters (DPF) to meet stricter EU4 and EU5 emissions standards. In fact, BMW started fitting DPFs as early as 2005/2006 on some models.
What is a DPF?
The purpose of the DPF is to trap soot particles from the exhaust system, preventing them from being released into the environment. When the filter becomes blocked, the vehicle’s ECU triggers a regeneration program that superheats the DPF to over 600°C, burning off the accumulated soot and converting it into harmless CO2 gas.
To trigger the regeneration process, the car must be driven at high speed for a sustained period, such as on a motorway or dual carriageway.
Problems with DPFs
Issues with DPFs typically occur in diesel cars that are used primarily for short or infrequent trips and rarely experience prolonged high-speed journeys. Urban driving or short trips often block the DPF more quickly, as the regeneration process cannot initiate or worse, is interrupted midway.
When the DPF becomes clogged, the orange warning light on the dashboard will illuminate, indicating that the DPF is about 70% blocked and no longer functioning correctly.
Steps to Address a DPF Warning Light
Plan a High-Speed Drive:
If the orange DPF light is illuminated, take the car for a high-speed drive on the motorway or dual carriageway.
Aim to drive at high RPMs for at least 30 minutes.
This will allow the ECU to trigger the DPF regeneration process, burn off the accumulated soot, and extinguish the warning light.
Delayed Regeneration Issues:
If the DPF light remains on or returns shortly after a motorway drive, the level of blockage, the time since the warning light first illuminated, or the age of the DPF may mean the regeneration process was unsuccessful.
Preventing DPF Issues
To avoid DPF problems:
Choose the Right Vehicle: Avoid diesel cars with DPFs if your driving mainly consists of short trips or urban driving. Diesel vehicles are better suited for regular long-distance motorway journeys.
Maintain Proper Operation: Regularly drive the car at high speeds to allow the DPF regeneration process to complete.
Advanced Diagnostics and Forced Regeneration
If the DPF warning light persists, BMW diagnostic software can help:
Check DPF Condition: Use the software to evaluate the state of the DPF and clear any stored fault codes.
Trigger Forced Regeneration: Manually initiate a DPF regeneration process before taking the car for a legal, high-speed drive on a quiet motorway.
Additional Features of BMW Diagnostic Software
View statistics on the distance travelled since the last DPF regeneration.
Conduct sensor tests and monitor backpressure exhaust readings.
Check and reset CBS (Condition-Based Servicing) parameters, such as oil quality, which can impact proper DPF operation.
Other Causes of DPF Issues
Some BMW diesel models may also experience issues due to:
Coolant Temperature Sensor:
A faulty sensor may prevent the engine from reaching the optimal temperature for DPF regeneration.
EGR Thermostat:
A malfunctioning EGR thermostat can keep the engine running below its ideal operating temperature, preventing regeneration.
Both components should be inspected and replaced if necessary to ensure proper DPF operation.
Cost of DPF Replacement
Replacing a clogged DPF can cost over £1,000 if the car is out of warranty, a significant portion of which is diagnostic labour. However, with BMW diagnostic software, you can perform many of these checks and procedures yourself from your driveway, saving time and money.
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