Hello, 5 months ago my 2003 CTS displayed the error "Service Steering System" and the steering became harder. I checked the power steering fluid and it was empty. I filled it with Dexron 3 (per the manual) and the message still hasn't went away. The steering is still hard as well. Did I ruin anything, or is there air in the system? I have cleared the code a couple of times, and even left it for 24 hours with the battery disconnected. I'm at a loss.