Off-Car DPF Cleaning: Citroen Picasso and Seat Alambra Case Study

Off-Car DPF Cleaning: Citroen Picasso and Seat Alambra Case Study Diesel Particulate Filters (DPFs) play a vital role in reducing harmful emissions from diesel engines. Over time, these filters collect soot and ash, which can cause blockages and affect engine performance. Many drivers rely on on-car cleaning methods to clear these issues, but sometimes that’s not enough—especially for cars that spend a lot of time idling or driving in town. In those cases, an off-car clean might be necessary to properly restore the filter. Diagnosing the Citroen Picasso DPF Issue For this Citroen Picasso, the driver previously had an on-car clean about two years ago. Recently, someone else attempted a DPF clean, but it only lasted for about 50 miles before the warning light returned. Checking the live data revealed: Average distance between regenerations: 115 miles (186 kilometres) DPF pressure reading: 32 mibars Fault codes: P2463: Particulate filter detected overloaded P246C: Particulate filter detected clogged The last regeneration was only 10 miles ago, yet pressure remained high. This pointed to a blockage that on-car cleaning could not fix. Damage or Ash Build-Up? The problem usually comes down to two possibilities. Either the DPF is physically damaged or it's full of ash after years of use. To find out, the DPF must be removed for a closer look. This step helps avoid unnecessary replacement costs and ensures the right cleaning method is chosen. Removing the DPF from the Citroen Picasso The DPF on this Citroen Picasso is located under the car, separate from the catalytic converter. Some vehicles have the catalyst and DPF combined, but this model is simpler to remove. The straightforward setup allows for quicker access and a less involved removal process. Seat Alambra: More Complex Cleaning Challenges The second vehicle in this case study is a Seat Alambra (also related to the Volkswagen Sharan 2.0L TDI), with a more complicated DPF design. Key features include: Three outlet ports instead of just one Clean inlet side, indicating no damage Heavy ash build-up from 250,000 miles of taxi service This design requires a careful approach to block all outlets during cleaning while ensuring no leaks. Back Flushing Method for Off-Car Cleaning To clean these filters, a back flushing technique is used. This means pushing water in reverse through the DPF to remove trapped ash. For the Seat Alambra, a cable-tied rubber glove was used as a makeshift seal, while extra ports were manually blocked during flushing. The process involves: Pressurizing a water tank connected to the DPF inlet Forcing water and an air/water mixture through to break down ash Watching for grey sand-like ash coming out, which is the main cause of blockages This technique gradually clears the ash, improving the filter’s function. Equipment Used: DCS16 Carbon Clean Machine The DCS16 machine from Carbon Clean makes the off-car cleaning process efficient. It fits inside a van and provides pressurized water and air for thorough flushing. This portability allows mobile service, reducing vehicle downtime. Link to DCS16 machine... DCS DPF Machines: Solutions for Diesel Particulate Filters https://share.google/gB1w8kC7pbRitgeuF Cleaning the Citroen Picasso DPF Off-Car The Citroen Picasso’s DPF has a simple design with one inlet and one outlet. It’s important to flush it in reverse—pushing water from the outlet back through to the inlet. During flushing: The DPF showed minimal soot but heavy ash presence Multiple flushes were needed to clear grey ash until the runoff water turned clear This rinse cycle highlights how ash, rather than soot, contributes most to blockage in some DPFs. Refitting and Resetting the ECU After cleaning, the DPF was refitted on the vehicle. The next step involves using a vehicle diagnostic tool such as the Launch Tab 3 Euro Tab 3 to: Tell the engine control unit (ECU) the DPF has been replaced or cleaned Reset fault codes Clear pressure sensor data so accurate readings can resume This reset ensures the vehicle recognises the clean filter and avoids false warnings. Monitoring Pressure Readings Post-Clean Immediately after reset, pressure readings may be high because of water still inside the DPF. To speed up drying and normalise readings: The engine revs were held at around 3,000 RPM for several minutes Pressure dropped from 93 mibars to 3 mibars, which is close to a new filter’s ideal reading Target pressure after cleaning falls between 2 and 6 mibars This confirms the cleaning was effective. Two Successful Off-Car Cleans Completed Both the Citroen Picasso and Seat Alambra filters were successfully cleaned off-car. These examples show how off-car cleaning can be the best solution where on-car methods fail or for filters heavily laden with ash. Efficient Setup and Professional Service