BMW E46 Diesel: Multiple Issues Point to Knock Sensor

Hey there! I've got some experience with BMWs having owned an '03 BMW 5 Series diesel. I'm no expert but I've dealt with my fair share of repairs. Had very similar symptoms with my car, and it turned out to be a loose connection in the wiring harness near the knock sensor. Took it to my regular workshop, they diagnosed it pretty quickly. Total bill was 95 Euro, mainly for tracking down and fixing that faulty connection. They just needed to clean and properly secure the plug. I've also owned a BMW 7 Series, so I'm quite familiar with how these engines behave when something's not right. Before I can give you more specific advice, could you share: Does the engine light flash or stay constant? When exactly did these symptoms start? Have you noticed any unusual sounds from the engine?

Thanks for sharing your experience! Currently at 174077 KM on my BMW 3 and just had a service last month. Had a similar wiring issue before, but this feels different. The engine light stays constant, and I've noticed a distinct knocking sound, especially during acceleration. It's definitely gotten worse over the past week. The rough idle is particularly noticeable when the engine's cold. Going to get it checked this week, but wanted to hear from others who've dealt with similar issues. Do you think I should mention the knock sensor specifically to the mechanic, or just let them diagnose it from scratch?

Hey again! Yeah, based on what you're describing, especially that knocking sound during acceleration, this does sound different from the wiring issue I dealt with on my 5 Series. With the constant engine light and those specific symptoms you're mentioning, I'm actually leaning towards it being the knock sensor itself rather than just a connection problem like I had. In my experience with BMWs (both my 5 and 7 Series), it's usually best to let the mechanic do their own diagnosis rather than suggesting specific parts. My regular mechanic actually appreciates when I describe the symptoms in detail rather than jumping to conclusions. The knocking sound you're hearing, combined with that rough cold idle, could point to several things. When my 5 Series started showing similar symptoms at around 180,000 KM, I initially thought it was the knock sensor too. But honestly, just describe exactly what you're experiencing, the knocking sound, the cold idle issue, and when it started getting worse. These details will help them pinpoint the actual problem faster. By the way, nice that you had a service last month, that should help narrow down what it isn't. Let us know what the mechanic finds, always good to share knowledge about these issues for other BMW owners!

Thanks so much for the detailed advice! You make a really good point about letting the mechanic do their own diagnosis. I'll definitely focus on describing the symptoms exactly as they're happening rather than suggesting it's the knock sensor. Actually feeling more confident about the repair visit now. It's super helpful hearing from someone who's owned multiple BMWs and dealt with similar issues. I'll make sure to document all the symptoms, the knocking sound, cold idle roughness, and how it's progressed over the week. You're right that the recent service should help rule some things out. I'll update the thread once I get it checked out. Really appreciate you taking the time to share your experience and advice. Fingers crossed it's something straightforward like in your case!