By mistake I left the truck in the ON position (engine not running) for about 1 day. I half noticed it the next day, started the truck, and saw what I thought was "check gauges" and assumed that would go out when the voltage stabilized on 14V. Then I noticed it was CEL. Temp, oil and voltage all fine. A 1999 has no pollution stuff. Engine seems to run OK. Have not read the code yet.