BMW 4 Diesel DPF Issues, Exhaust Temp Sensor Problems?

Hey there! I had some experience with a similar issue on my 2015 BMW 3 Series diesel (had a 5 Series before that). I have some basic car knowledge, mostly from dealing with my own repairs over the years. Last winter, I faced almost identical symptoms, limp mode, check engine light, poor performance, the works. Took it to my workshop thinking it was the temp sensor, but they actually found a crack in the exhaust system causing a leak. Fixed it for about 265 Euro, and all those issues disappeared completely. Before jumping to conclusions about the sensor, can you tell us if you're hearing any unusual exhaust sounds or noticed any black residue around the exhaust joints? Also, what's the mileage on your 4 Series? These details would help figure out if you're dealing with the same problem I had. Let me know these details, and I might be able to share more specific info from my experience!

Hey, thanks for the detailed response! My BMW's at 14918 KM and just had its service last month. I haven't noticed any black residue, but now that you mention it, there's a slight whistling sound when accelerating. Maybe I should check for exhaust leaks first before replacing the sensor. Appreciate you sharing your experience with the cracked exhaust, definitely gives me something else to consider. I'll have my mechanic take a look at the exhaust system during inspection. Did your car also struggle with DPF regeneration when you had the exhaust leak?

Hey again! Yes, absolutely, when I had that exhaust leak, my DPF regeneration was totally messed up. The system needs proper back pressure to work correctly, and that crack was throwing everything off. Actually, that whistling sound you're describing is exactly what I heard before finding the leak in my car. The fact that your car's pretty fresh from service is interesting though, might be worth checking if anything got knocked loose during the service work. When they were working on my BMW, they found that the crack was right near one of the connection points, probably from some stress on the system. One thing I learned from my experience, these symptoms can be super misleading. I was so convinced it was the temp sensor that I almost ordered one online to replace it myself! Glad I didn't waste that money. The exhaust leak was causing similar readings to a faulty sensor because the system wasn't getting accurate pressure and temperature data. My suggestion? Get someone to do a proper pressure test on your exhaust system. That's how they found my leak. Better to rule out the simple stuff before replacing sensors. Keep me posted on what you find, I'm really curious if it turns out to be the same issue!

Thanks so much for the helpful advice! You've honestly saved me from potentially wasting money on a new sensor without checking the more obvious issues first. That pressure test sounds like the way to go, especially since my whistling noise matches what you experienced. I've just booked the car in for next week, and I specifically asked them to check the exhaust system and do a pressure test. I'm actually feeling quite relieved now, if it is just an exhaust leak, it shouldn't be too expensive to fix. I'll definitely focus on checking those connection points, especially around where they worked during the recent service. You're right about symptoms being misleading. I was so fixated on the sensor being the problem that I might have missed these other signs. Really appreciate you taking the time to share your experience, it's been super helpful. I'll update the forum once I get it checked out so others can learn from this too!