touchscreen misbehavior

My touchscreen stopped responding, and I was planning to replace it, but then realized that the the screen was working but calibration had gone way off – touching the screen at the far left edge would activate a button at the far right. I'm sometimes able to correct the problem by going into the diagnostic screen (hold down info button while turning on and off headlights five times), but the problem returns next time I start the car. So it appears that a computer controlling the screen is malfunctioning, but I don't know if this computer is contained in the screen assembly, or is located elsewhere. Thanks for any hints!