Crosstrek DPF Failure Causing Power Loss & Smoke Issues

As a hobby mechanic with some experience working on diesel engines, I faced a very similar issue with my 2015 Subaru Forester diesel last year. The symptoms matched exactly what you describe, reduced power, smoke during acceleration, and warning lights. The low pressure readings from the particulate filter system were also identical to your situation. After diagnostic testing, the workshop identified a faulty exhaust back pressure sensor. This sensor is crucial for proper DPF regeneration cycles. When it fails, the engine computer receives incorrect readings, leading to improper particulate filter operation and the symptoms you describe. The repair cost was 245€ including parts and labor. Since the fix, the engine runs perfectly and all warning lights cleared. The DPF regeneration process now works as intended. Before suggesting specific solutions, could you share: current mileage, Service history, especially recent DPF maintenance, Exact warning lights displayed, any recent changes in driving patterns This information would help determine if your issue is identical to what I experienced with the pressure sensor failure.

Thanks for explaining what you found. My mileage is at 118412 KM with regular maintenance done every 20000 KM, last service completed 2 months ago. In addition to what I shared before, the dashboard shows both the DPF warning light and emission control warning light flashing. I mainly do highway driving, but recently had more city trips which might affect the DPF regeneration cycles. The particulate filter warning appeared first, followed by reduced power and visible smoke about a week later. Getting similar low pressure readings as you mentioned makes me think the exhaust system sensor could indeed be the culprit. Will have the workshop check the back pressure sensor specifically.

Thanks for providing those details. Given your driving pattern change and the sequence of warning lights, it matches my Forester case even closer than I initially thought. The shift from highway to city driving often disrupts normal DPF regeneration cycles. However, a properly functioning back pressure sensor should still manage this transition. When my sensor failed, the emission control system also showed similar progressive symptoms, first the DPF light, then reduced power and smoke. One important observation from my repair experience: the low exhaust pressure readings combined with recent urban driving created a false impression of a clogged particulate filter. The mechanic found the filter itself was actually fine, the sensor was sending incorrect data to the engine management system. The repair resolved all symptoms: Warning lights cleared, Normal power restored, No more smoke during acceleration, Proper DPF regeneration resumed Given your similar maintenance schedule and symptoms progression, I strongly suspect the same sensor issue. A professional diagnostic check focusing on the exhaust back pressure sensor would be the logical next step.

Thanks everyone for the detailed insights. After comparing all the symptoms and scenarios, I feel much more confident about the likely cause now. The matching pattern of warning lights, smoke, and especially the low pressure sensor readings really points to the same exhaust back pressure sensor issue discussed here. What convinced me most was how the symptoms developed in the same sequence, first the DPF regeneration warnings, then power loss and smoke, all while showing those suspicious pressure readings. The emission control system behavior matches exactly what was described. Will book the car in next week and specifically ask them to check the exhaust system pressure sensor. The fact that the actual DPF was fine in the other case despite similar symptoms is really helpful to know. Good to hear the repair solved all issues without needing major exhaust system work. Based on the great advice here, I expect to face a straightforward sensor replacement rather than extensive DPF or emission control system repairs. Will update once the workshop confirms the diagnosis.