To be absolutely certain:
* Consult your owner's manual: This is the best resource for the precise location in your specific vehicle.
* Use a repair manual: A Haynes or Chilton manual for your year and model Malibu will show diagrams and instructions.
* Search online forums: Searching for "1999 Chevy Malibu PCM location" on automotive forums like ChevyTalk or others might reveal pictures and descriptions from other owners who have accessed their PCM.
Be careful when working near the dashboard, as there are several sensitive electrical components. If you are not comfortable working on your vehicle yourself, it's best to have a qualified mechanic locate it for you.