Loud Cadillac STS Exhaust Points to Faulty Flap System

I had a very similar issue with my 2013 Cadillac CTS last winter. As someone with moderate experience working on cars, I initially thought it was just a loose exhaust component, but it turned out to be more complex. The symptoms matched yours exactly, loud exhaust noise during cold starts and a stored fault code. After checking, my workshop confirmed the exhaust valves were malfunctioning. The electrical actuator controlling the exhaust flap had failed, causing improper exhaust flow control. The repair involved replacing the faulty exhaust flap actuator and recalibrating the system. Total cost came to 190€ including parts and labor. Since the fix, the exhaust noise returned to normal levels and the fault code hasn't returned. Before suggesting specific solutions, could you share: Has the check engine light come on? Does the noise change at different engine speeds? Have you noticed any loss in performance? Can you hear any rattling from the exhaust components? This information would help determine if your exhaust blockage issue is similar to what I experienced or if it might be something else in the exhaust system.

Thanks for the helpful diagnosis information. I also had the check engine light come on last week, and the noise definitely varies with engine speed. There is a slight performance loss, especially during acceleration. I can hear some rattling near the rear of the car. Since my last service at 89020 KM, the engine performance has gradually declined. The exhaust system noise gets particularly loud when the engine is cold, suggesting the flap motor might indeed be the culprit. Glad to hear your repair was relatively straightforward. Based on your experience, I will have the exhaust valves checked first before exploring other potential issues with the exhaust system.

Based on those additional symptoms, it sounds exactly like the issue I faced with my CTS. The combination of check engine light, variable noise with engine speed, and performance loss strongly points to the exhaust flap actuator failure I experienced. The rattling you mention near the rear matches what I heard before the repair. My exhaust flap motor had completely seized, causing the valve to stay in one position. This created uneven exhaust flow and that characteristic cold start noise. Since getting the exhaust repair done, my engine performance returned to normal. The workshop identified that the flap actuator had accumulated carbon deposits, a common issue in our model. They recommended regular exhaust system checks during maintenance to prevent future failures. The gradual performance decline you mentioned also matches my experience. The exhaust components tend to deteriorate slowly, making it less noticeable until the symptoms become more severe. In my case, the complete repair process took about 3 hours, and the car has been running perfectly for the past 8 months. Your mileage is similar to when my issue occurred, suggesting this might be a common wear point for these exhaust system components.

Thanks for sharing your experience in such detail. The similarities between our cases are really striking, especially regarding the exhaust system symptoms. Your recommendation to check the exhaust valves first makes perfect sense given the pattern of problems. After hearing about your successful repair, I feel more confident about getting this fixed. The declining engine performance and loud exhaust noise during cold starts match your situation exactly. It helps knowing the repair is relatively straightforward and took only 3 hours in your case. I will schedule an appointment with my workshop to have them specifically check the exhaust flap actuator and look for carbon deposits. The fact that regular exhaust system maintenance can prevent future issues is good to know. Given the similar mileage when these problems occurred, this seems like a typical wear pattern for our models. Really appreciate you taking the time to explain your experience in detail. This has saved me a lot of worry about potential major exhaust repair costs. Will update once I get the car checked and hopefully fixed.