GL8 Rough Idle Points to Faulty Knock Sensor Issue

As someone with some repair experience, I had a similar issue with a Buick LaCrosse from around the same period. The symptoms you describe strongly align with knock sensor problems, which I encountered as well. My engine knock issues started with rough idling and the check engine light, followed by decreased fuel efficiency. After checking with my regular workshop, they found the knock sensor connection was loose, with a damaged wire in the sensor harness. The total repair cost was 95 Euro for diagnosing and fixing the cable connection issue. The symptoms you describe, rough idle, increased fuel consumption, and the malfunction light, point toward a potential knock sensor problem, but could also indicate other issues. To provide more specific guidance, could you share: Build year of your GL8, Current mileage, Engine size, Any engine codes showing, Any unusual sounds, especially during acceleration, When was the last routine maintenance performed While my LaCrosse issue was resolved by repairing the wiring, its important to get a proper diagnosis since similar symptoms can stem from various engine problems. Consider having a diagnostic scan done to confirm if its actually the knock sensor before proceeding with repairs.

Thanks for the detailed response. For reference, Im running a 2016 Buick GL8 with 174078 KM on the clock. Just to add to the auto repair discussion, I did notice a slight knocking sound during acceleration which seems relevant. The warning light started flashing right after my last service about 3 weeks ago. I will definitely get those engine codes checked as suggested. Anyone here know a ballpark cost for knock sensor replacement if that turns out to be the culprit?

Thanks for providing those additional details about your 2016 GL8. That knocking sound during acceleration, combined with the timing of the warning light after your service, definitely reinforces the knock sensor theory. When I had similar symptoms with my LaCrosse, the knocking noise was quite similar to what you describe. The diagnosis proved that poor performance was indeed linked to faulty knock sensor signals, which caused incorrect ignition timing adjustments. A complete knock sensor replacement for these models typically runs between 150-300 depending on parts quality and labor rates. However, as in my case, sometimes the issue can be resolved by repairing wiring or connections at a much lower cost. Since your symptoms started after a service, it might be worth checking if any work was done near the knock sensor area, as connections sometimes get disturbed during routine maintenance. The fact that you have both the sound and the fuel efficiency issues makes me more confident in the knock sensor diagnosis, based on my similar experience. Would recommend getting those codes read first, that will help confirm if its genuinely a knock sensor problem or potentially something else affecting engine performance.

Thanks everyone for the input. I got the codes checked today and it showed P0325, which from what I understand confirms the knock sensor problem. Really helpful to know the typical cost range of 150-300 for the replacement. Given all the symptoms match up, the engine knock sound, warning light, and poor fuel efficiency, I feel pretty confident moving forward with the repair. Will probably get it done next week and update the forum with how it went. The timing of this starting right after my service makes me wonder if something got knocked loose during maintenance. At least its not looking like a major engine issue, which was my initial worry when the check engine light first came on.