The external temp. read out appears on the top line of the radio display. On the far right side of the radio is the info button, it has an up, and down arrow on the button. Each time an arrow button is pressed, a different display will appear on the top line of the radio. ex, trip odometer, engine oil life,etc. The external air temp is one of these displays. It will display this info even if the radio is turned off. Hope this helps, good luck with your CTS,they are sure fun to drive.
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