check engine light and code 21

Hello, it looks like obd1 GM code 21 is the TPS out of range, this will be your throttle position sensor. The TPS measures the amount of throttle plate opening or angle and relates this information to the engine computer. This combined with other measurements from other sensors determines the amount of fuel added to the system. Most likely the TPS has failed unless you find a wiring issue. The TPS is located on the throttle body and should be a 2 or 3 wire sensor. I believe the Cadillac brougham from 1987-1991 had a carburetor so it might just be a throttle switch versus a position sensor. But either way that's what code 21 is. This is the original part number 17078448 from GM.