BMW M2 Check Engine Light and Rough Idle Mystery

Hey there, fellow BMW owner here with a 2019 M4. Had almost identical symptoms last summer at around 65k km. Initially thought it was the water sensor too, but turned out it was actually a faulty wiring connection to the crankshaft position sensor. The check engine light and rough running were exactly as you described. The connector had corroded and wasn't making proper contact. Initially, my mechanic wanted to replace the entire sensor unit, but after a thorough inspection, we found it was just the wiring harness connection that needed fixing. It wasn't a major repair but definitely required someone who knows BMW electronics well. My advice would be to have someone check the wiring connections first before replacing any sensors. These symptoms are pretty typical for electrical connection issues in our engines. Not a catastrophic problem, but you'll want to get it sorted soon to prevent any potential damage to other components. Just make sure whoever works on it has proper BMW diagnostic tools and experience with M series cars, that's crucial for accurate troubleshooting.

Thanks for sharing your experience with the M4! Really good to hear it wasn't anything major. My symptoms do sound exactly like what you had. Quick question, do you remember roughly how much you ended up paying for the wiring harness repair? Also, has everything been running smoothly since then, or have you noticed any other issues pop up? Just wanna know what to expect cost-wise and if I should be looking out for anything else.

Hey again! Great news, I actually just got my M2 back from the mechanic last week, and it turned out to be exactly what I suspected when I first replied to your post. The water sensor was indeed the culprit, but thankfully it wasn't the sensor itself that needed replacing. Just like I mentioned before about checking connections first, it was just a faulty cable connection that needed fixing. Total bill came to 95 €, way less scary than a full sensor replacement! The car's running perfectly smooth now, no check engine light, no rough running, just purring like a kitten. Haven't had a single problem since the repair. This really reinforces what I said in my first reply about getting those connections checked before jumping to replacing parts. Since you're having such similar symptoms, I'd definitely recommend having your mechanic look at the wiring connections first. Could save you some serious cash! And to answer your question about other issues, nope, haven't had any other problems pop up since getting it sorted. These BMWs are pretty solid once you fix what's actually wrong instead of just throwing parts at them.

Just wanted to update everyone. I took my M2 to a new mechanic yesterday, and wow, what a different experience! I explained everything, including what you guys suggested about checking the wiring first. The mechanic found the same issue, just a corroded connection near the crankshaft sensor. The repair cost was super reasonable, much less than what I feared. The whole job took about two hours, and the car's running perfectly now. No more check engine light, and that annoying rough running is completely gone. Such a relief it wasn't anything major! Really grateful for the advice about finding someone who knows BMWs well. This new mechanic actually took the time to show me what was wrong and explained everything clearly. Way better than my last experience where they just wanted to replace everything without checking. I've put about 500km on it since the repair, and it's running like new. Looks like you guys saved me from getting ripped off again. Thanks for all the help!