2005 Cadillac CTS Owner's Manual - Page 171

Tire Pressure Light This light will come on if the system detects low tire pressure. Malfunction Indicator Lamp Check Engine Light Your vehicle is equipped with a computer which monitors operation of the fuel, ignition, and emission control systems. This light will also come on for a bulb check when the vehicle is started. See Tire Pressure Monitor System (CTS-V) on page 5-65 for more information. For more information on the proper tire pressure, see Loading Your Vehicle on page 4-33. For more information on your tires, see Tires on page 5-54. This system is called OBD II (On-Board Diagnostics-Second Generation) and is intended to assure that emissions are at acceptable levels for the life of the vehicle, helping to produce a cleaner environment. The check engine light comes on to indicate that there is a problem and service is required. Malfunctions often will be indicated by the system before any problem is apparent. This may prevent more serious damage to your vehicle. This system is also designed to assist your service technician in correctly diagnosing any malfunction. Notice: If you keep driving your vehicle with this light on, after awhile, your emission controls may not work as well, your fuel economy may not be as good, and your engine may not run as smoothly. This could lead to costly repairs that may not be covered by your warranty. 3-45