Check the electric harness/pigtail connectors to the struts. They're monitored and active suspension components. Unplugged, removed, chafed is code time.
What is the build date on your 2002 STS ? Driver's door sticker - it makes a BIG difference in diagnosis. Look on the RPO sticker under the spare tire cover - is the suspension type code F45 (CVRSS) or F55 (MRC) ?
OK - Your (our) cars have the "Lord/DELPHI Magnetic Ride Control suspension system" - Google that for info. The last of the 2002 (from 01-15-02) and all 2003 STSonly had the system and were the test mules for the installs in Corvette and Ferrari, later development went into upscale GM and other sports vehicles.
The system was the progression from the CVRSS suspension controls and uses no moving parts (save the piston and barrel) for fluid control - the fluid is a magnetically influenced liquid that can change from about 10W oil to jelly in less than .001 second - constantly.
Study it and the owner's manual as well as learn to DRIVE the car - the handling chararacteristics in tight road work will amaze you. It will NOT have anything close to a "Cadillac ride". It's a performance suspension and it feels like it - all the time.
Your car uses MANY sensors for suspension and body control - roll, pitch, yaw, desired turn radius, actual turn radius, wheel slip, wheel spin, wheel speed, power output, gear selection - and on and on. The "normal force" codes may refer to a wiring harness being disconnected from the struts (front struts, rear shocks with level control) - or someone has cheaped out and installed the wrong struts and the system is responding to the "fix".
The struts and wheel hubs may have as many as 3 wiring pigtails attached - wheel speed sensor, brake pad wear sensor, strut control.
BTW - a real replacement strut for our cars costs from $650 to $1200 each, depending on source. Shocks are a bit less.