WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
On Century and Grand Prix, PCM is located left side of engine compartment, inside air cleaner assembly. See Figure. On Malibu, PCM is located under Instrument Panel (I/P), next to Data Link Connector (DLC). See Figure.