Whenever your car shows you a CAL message in the driver information center, it means that the compass system is out of calibration. To fix this, drive your vehicle for a short distance in open area where it can get a GPS signal. The DIC will then calibrate itself and show you a correct heading on the display. Some systems require calibration more often than others, such as the odometer or speedometer if you replace your wheels and tires, airbags, ABS system, and TPMS sensors.
Illegal modifications to the engine control units can impact the emissions control system. When the computer's program is modified, it generates a new Calibration Identification Number (Cal ID) and a new Calibration Verification Number (CVN). These numbers are used to identify and track the program's history.