M4 CEL and Rough Running: Exhaust System Crisis?

Hey there! I had a similar issue with my 2018 BMW M3 last year (I have some experience working on cars as a hobby). The symptoms you're describing sound exactly like what I went through, check engine light, poor performance, and that nasty exhaust smell. Turned out it was a faulty lambda sensor. Got it fixed at my trusted workshop, cost me about 375 Euro including parts and labor. The car's been running smoothly ever since. Before suggesting anything specific though, could you share: Any error codes you're getting? How many miles/kilometers on your M4? When did these symptoms first appear? Have you had any recent work done on the exhaust system? With these details, I might be able to help confirm if it's the same issue I had with my M3. The M series can be tricky, but usually these symptoms point to a few specific issues.

Hey there! I had a similar issue with my 2018 BMW M3 last year (I have some experience working on cars as a hobby). The symptoms you're describing sound exactly like what I went through, check engine light, poor performance, and that nasty exhaust smell. Turned out it was a faulty lambda sensor. Got it fixed at my trusted workshop, cost me about 375 Euro including parts and labor. The car's been running smoothly ever since. Before suggesting anything specific though, could you share: Any error codes you're getting? How many miles/kilometers on your M4? When did these symptoms first appear? Have you had any recent work done on the exhaust system? With these details, I might be able to help confirm if it's the same issue I had with my M3. The M series can be tricky, but usually these symptoms point to a few specific issues.

Hey there! I had a similar issue with my 2018 BMW M3 last year (I have some experience working on cars as a hobby). The symptoms you're describing sound exactly like what I went through, check engine light, poor performance, and that nasty exhaust smell. Turned out it was a faulty lambda sensor. Got it fixed at my trusted workshop, cost me about 375 Euro including parts and labor. The car's been running smoothly ever since. Before suggesting anything specific though, could you share: Any error codes you're getting? How many miles/kilometers on your M4? When did these symptoms first appear? Have you had any recent work done on the exhaust system? With these details, I might be able to help confirm if it's the same issue I had with my M3. The M series can be tricky, but usually these symptoms point to a few specific issues.

Hey there! I had a similar issue with my 2018 BMW M3 last year (I have some experience working on cars as a hobby). The symptoms you're describing sound exactly like what I went through, check engine light, poor performance, and that nasty exhaust smell. Turned out it was a faulty lambda sensor. Got it fixed at my trusted workshop, cost me about 375 Euro including parts and labor. The car's been running smoothly ever since. Before suggesting anything specific though, could you share: Any error codes you're getting? How many miles/kilometers on your M4? When did these symptoms first appear? Have you had any recent work done on the exhaust system? With these details, I might be able to help confirm if it's the same issue I had with my M3. The M series can be tricky, but usually these symptoms point to a few specific issues.

Thanks for reaching out! I'm getting similar issues after my latest service, currently at 99590 KM. The symptoms started about a week ago, pretty suddenly actually. No recent work on the exhaust system, but I'm getting error code P0420 on my OBD scanner. Based on what you're describing with your M3, it does sound pretty similar to my situation. I'm hoping it's just the lambda sensor like in your case, rather than something more serious with the catalytic converter. Did you notice any performance improvements immediately after your repair? Just trying to gauge if I'm dealing with the same thing here.

Thanks for reaching out! I'm getting similar issues after my latest service, currently at 99590 KM. The symptoms started about a week ago, pretty suddenly actually. No recent work on the exhaust system, but I'm getting error code P0420 on my OBD scanner. Based on what you're describing with your M3, it does sound pretty similar to my situation. I'm hoping it's just the lambda sensor like in your case, rather than something more serious with the catalytic converter. Did you notice any performance improvements immediately after your repair? Just trying to gauge if I'm dealing with the same thing here.

Thanks for reaching out! I'm getting similar issues after my latest service, currently at 99590 KM. The symptoms started about a week ago, pretty suddenly actually. No recent work on the exhaust system, but I'm getting error code P0420 on my OBD scanner. Based on what you're describing with your M3, it does sound pretty similar to my situation. I'm hoping it's just the lambda sensor like in your case, rather than something more serious with the catalytic converter. Did you notice any performance improvements immediately after your repair? Just trying to gauge if I'm dealing with the same thing here.

Thanks for reaching out! I'm getting similar issues after my latest service, currently at 99590 KM. The symptoms started about a week ago, pretty suddenly actually. No recent work on the exhaust system, but I'm getting error code P0420 on my OBD scanner. Based on what you're describing with your M3, it does sound pretty similar to my situation. I'm hoping it's just the lambda sensor like in your case, rather than something more serious with the catalytic converter. Did you notice any performance improvements immediately after your repair? Just trying to gauge if I'm dealing with the same thing here.

Hey again! Yeah, based on that P0420 code and your mileage, it definitely sounds like what I dealt with on my M3. When I got mine fixed, the performance improvement was almost instant, like night and day difference. The throttle response went back to being crisp, and that annoying exhaust smell completely disappeared. You know what's interesting? After my lambda sensor was replaced, I actually gained back some of the power I didn't even realize I'd lost. It's like when something goes wrong gradually, you don't notice how bad it gets until it's fixed. Just a heads up though, while my issue was the lambda sensor, that P0420 code can sometimes mean catalyst efficiency issues too. I got lucky that it was just the sensor, but you might want to have both checked out. My mechanic actually tested the catalyst while he was in there, just to be safe. One thing that really helped confirm it was the sensor in my case was using a diagnostic tool to look at the sensor voltage readings. They were all over the place, which is a classic sign of a failing sensor. Have you noticed any rattling sounds from your exhaust area? That might help narrow down if it's just the sensor or something else. In my case, there wasn't any rattling, which helped point toward the sensor being the culprit.

Hey again! Yeah, based on that P0420 code and your mileage, it definitely sounds like what I dealt with on my M3. When I got mine fixed, the performance improvement was almost instant, like night and day difference. The throttle response went back to being crisp, and that annoying exhaust smell completely disappeared. You know what's interesting? After my lambda sensor was replaced, I actually gained back some of the power I didn't even realize I'd lost. It's like when something goes wrong gradually, you don't notice how bad it gets until it's fixed. Just a heads up though, while my issue was the lambda sensor, that P0420 code can sometimes mean catalyst efficiency issues too. I got lucky that it was just the sensor, but you might want to have both checked out. My mechanic actually tested the catalyst while he was in there, just to be safe. One thing that really helped confirm it was the sensor in my case was using a diagnostic tool to look at the sensor voltage readings. They were all over the place, which is a classic sign of a failing sensor. Have you noticed any rattling sounds from your exhaust area? That might help narrow down if it's just the sensor or something else. In my case, there wasn't any rattling, which helped point toward the sensor being the culprit.

Hey again! Yeah, based on that P0420 code and your mileage, it definitely sounds like what I dealt with on my M3. When I got mine fixed, the performance improvement was almost instant, like night and day difference. The throttle response went back to being crisp, and that annoying exhaust smell completely disappeared. You know what's interesting? After my lambda sensor was replaced, I actually gained back some of the power I didn't even realize I'd lost. It's like when something goes wrong gradually, you don't notice how bad it gets until it's fixed. Just a heads up though, while my issue was the lambda sensor, that P0420 code can sometimes mean catalyst efficiency issues too. I got lucky that it was just the sensor, but you might want to have both checked out. My mechanic actually tested the catalyst while he was in there, just to be safe. One thing that really helped confirm it was the sensor in my case was using a diagnostic tool to look at the sensor voltage readings. They were all over the place, which is a classic sign of a failing sensor. Have you noticed any rattling sounds from your exhaust area? That might help narrow down if it's just the sensor or something else. In my case, there wasn't any rattling, which helped point toward the sensor being the culprit.

Hey again! Yeah, based on that P0420 code and your mileage, it definitely sounds like what I dealt with on my M3. When I got mine fixed, the performance improvement was almost instant, like night and day difference. The throttle response went back to being crisp, and that annoying exhaust smell completely disappeared. You know what's interesting? After my lambda sensor was replaced, I actually gained back some of the power I didn't even realize I'd lost. It's like when something goes wrong gradually, you don't notice how bad it gets until it's fixed. Just a heads up though, while my issue was the lambda sensor, that P0420 code can sometimes mean catalyst efficiency issues too. I got lucky that it was just the sensor, but you might want to have both checked out. My mechanic actually tested the catalyst while he was in there, just to be safe. One thing that really helped confirm it was the sensor in my case was using a diagnostic tool to look at the sensor voltage readings. They were all over the place, which is a classic sign of a failing sensor. Have you noticed any rattling sounds from your exhaust area? That might help narrow down if it's just the sensor or something else. In my case, there wasn't any rattling, which helped point toward the sensor being the culprit.

Thanks for the detailed response! After hearing your experience, I'm feeling a bit more optimistic about my situation. I haven't noticed any rattling sounds actually, which does line up with your sensor diagnosis. I did a bit more digging with my OBD reader after your suggestion about voltage readings, and you're right, the numbers are jumping around like crazy. I'm gonna book it in with my mechanic tomorrow and specifically ask them to check both the lambda sensor and catalyst, just to be thorough. You know, now that you mention the gradual power loss thing, I realize I've probably been driving with reduced performance for a while without even noticing it. It's like when you get used to something being slightly off until it gets really bad. Really hoping I'll experience that same night and day difference you did after the repair. Really appreciate you sharing your experience, it's given me a much clearer picture of what I might be dealing with. I'll update once I get it checked out. Thanks again for your help!

Thanks for the detailed response! After hearing your experience, I'm feeling a bit more optimistic about my situation. I haven't noticed any rattling sounds actually, which does line up with your sensor diagnosis. I did a bit more digging with my OBD reader after your suggestion about voltage readings, and you're right, the numbers are jumping around like crazy. I'm gonna book it in with my mechanic tomorrow and specifically ask them to check both the lambda sensor and catalyst, just to be thorough. You know, now that you mention the gradual power loss thing, I realize I've probably been driving with reduced performance for a while without even noticing it. It's like when you get used to something being slightly off until it gets really bad. Really hoping I'll experience that same night and day difference you did after the repair. Really appreciate you sharing your experience, it's given me a much clearer picture of what I might be dealing with. I'll update once I get it checked out. Thanks again for your help!

Thanks for the detailed response! After hearing your experience, I'm feeling a bit more optimistic about my situation. I haven't noticed any rattling sounds actually, which does line up with your sensor diagnosis. I did a bit more digging with my OBD reader after your suggestion about voltage readings, and you're right, the numbers are jumping around like crazy. I'm gonna book it in with my mechanic tomorrow and specifically ask them to check both the lambda sensor and catalyst, just to be thorough. You know, now that you mention the gradual power loss thing, I realize I've probably been driving with reduced performance for a while without even noticing it. It's like when you get used to something being slightly off until it gets really bad. Really hoping I'll experience that same night and day difference you did after the repair. Really appreciate you sharing your experience, it's given me a much clearer picture of what I might be dealing with. I'll update once I get it checked out. Thanks again for your help!

Thanks for the detailed response! After hearing your experience, I'm feeling a bit more optimistic about my situation. I haven't noticed any rattling sounds actually, which does line up with your sensor diagnosis. I did a bit more digging with my OBD reader after your suggestion about voltage readings, and you're right, the numbers are jumping around like crazy. I'm gonna book it in with my mechanic tomorrow and specifically ask them to check both the lambda sensor and catalyst, just to be thorough. You know, now that you mention the gradual power loss thing, I realize I've probably been driving with reduced performance for a while without even noticing it. It's like when you get used to something being slightly off until it gets really bad. Really hoping I'll experience that same night and day difference you did after the repair. Really appreciate you sharing your experience, it's given me a much clearer picture of what I might be dealing with. I'll update once I get it checked out. Thanks again for your help!