2004 GMC Sierra 1500 Pickup Owner's Manual - Page 247

Radio Messages CAL ERR (Calibration Error): Your audio system has been calibrated for your vehicle from the factory. If CAL ERR appears on the display, it means that your radio has not been configured properly for the vehicle and must be returned to the dealer for service. LOCKED: This message is displayed when the THEFTLOCK® system has locked up. You must return to the dealer for service. XM™ Radio Messages Radio Display Message XL (Explicit Language Channels) Condition XL on the radio display, after the channel name, indicates content with explicit language. Updating encryption code Loss of signal Action Required These channels, or any others, can be blocked at a customer's request, by calling 1-800-852-XMXM (9696). Updating The encryption code in your receiver is being updated, and no action is required. This process should take no longer than 30 seconds. Your system is functioning correctly, but you are in a location that is blocking the XM signal. When you move into an open area, the signal should return. Your radio system is acquiring and processing audio and text data. No action is needed. This message should disappear shortly. This channel is not currently in service. Tune to another channel. No Signal Loading XM Acquiring channel audio (after 4 second delay) Channel not in service CH Off Air 3-83