Cadillac DTS Knock Sensor Issues and Rough Idle Fix

Had a similar issue with my 2013 Cadillac XTS last month. I have some experience working on cars, mostly basic maintenance and diagnostics. The check engine light came on and I noticed the same symptoms, rough idling and decreased fuel efficiency. Initially thought it might be something more serious, but the mechanic found it was just a loose connection at the knock sensor plug. The repair cost was 95€, which covered diagnostic time and fixing the cable connection. No parts needed replacement, just needed to clean and secure the connection properly. The malfunction indicator turned off right after the fix and the engine has been running smoothly since. Before you head to a shop, have you checked for any other warning lights? Does the rough idle happen more when the engine is cold or warm? Have you noticed any unusual engine sounds? Are you using the recommended fuel grade? The knock sensor issue is pretty common on these engines, but its always good to get a proper diagnosis since similar car problems can have multiple causes.

Thanks for sharing your experience. After 198091 KM, I can confirm the rough idle is most noticeable when the engine is cold and gets slightly better after warming up. There are no other warning lights besides the check engine light. The engine knock becomes more apparent under acceleration, especially when using regular fuel instead of premium. I will get it properly checked at my next service appointment. Your insight about the loose connection is helpful, will have them inspect that first before replacing parts unnecessarily. The fuel efficiency drop has been quite significant, so hoping its just a sensor issue rather than something more serious.

Thanks for the update on your Cadillac symptoms. After fixing the knock sensor connection on my XTS, I had similar cold start issues return about 6 months later. This time it turned out to be the actual knock sensor failing, not just a connection issue. The poor performance during cold starts and knocking under acceleration are classic signs. The repair cost was higher, around 280€ for the part and labor. But the improvement in fuel efficiency alone made it worth fixing. My fuel consumption dropped back to normal within two tanks. Just a heads up, make sure they check the wiring harness thoroughly when replacing the sensor. In these engines, the harness can get brittle over time and cause intermittent malfunction indicator triggers even with a new sensor. The combination of cold start issues, engine knock, and increased fuel consumption matches almost exactly what I experienced. Switching to premium fuel helped reduce the symptoms temporarily, but the underlying car problems remained until the sensor was replaced. Definitely get it checked soon, driving with a faulty knock sensor for too long can lead to engine damage since it cant properly adjust timing to prevent detonation.

Thank you all for the detailed responses. Just wanted to update that I took my DTS to the shop today. The diagnostic confirmed a faulty knock sensor, and they found some damaged wiring as well. Total repair came to 320€ for parts and labor. The car problems have completely resolved, no more check engine light, the rough idle is gone, and fuel efficiency has improved significantly. The mechanic showed me the old sensor which was clearly corroded. They also replaced part of the wiring harness since it was starting to crack. Was worth fixing it promptly. The engine runs much smoother now, especially during cold starts. Premium fuel seems to make an even bigger difference with the new sensor working properly. Glad I didnt wait any longer as the mechanic mentioned possible engine damage if left unchecked. Will definitely keep an eye on the warning lights and fuel consumption going forward to catch any issues early. Thanks again for helping confirm my initial diagnosis, saved me some diagnostic time at the shop.