1999 Cadillac Deville how do you clear the codes on the das

After you get them read, press fan down to scoll through available modules, fan up to select a module, fan down again to scrlll available command, and fan up again to execute. Some modules will only allow reading and clearing codes, where others will show inputs/outputs, and allow override function tests. For example: You have entered diagnostics by pressing off and warmer on the climate panel. After the segment check in goes through a code display, you have a P0603(for instance). Once all the available modules display codes, the display reads "PCM ". You press fan up and the display says "PCM CODES", you press fan down once and the display reads "PCM CLEAR CODES". Press fan up and after a few seconds "PCM CODES CLEAR" displays and your done. You can exit diagnostics by key off, or pressing recirc button(or maybe econ). Fan up, and fan down will accomplish all commands, unless you read data, or perform overrides, and that is another, more lengthy, story.