Would you believe flash reprogrammable PCMs have been in vehicles for more than a decade? The first such application was the 1990 Geo Storm. Why a humdrum car like the Storm would be the first to receive a flash reprogrammable computer system is unknown. You'd think GM would have chosen a more high profile vehicle like a Cadillac or Corvette to usher in the new technology. But they didn't. The choice probably had more to do with production scheduling and new model introductions than profile or image. GM knew OBD II was coming and that it would require a new generation of PCMs that were faster, more capable and able to be programmed electronically.

Up to this point, Program Read Only Memory (PROM) chips held all of the PCM's vital calibration information and operating instructions. GM pioneered the replaceable PROM chip as a way of programming a limited number of basic PCMs to fit a wide range of GM makes and models. A replaceable PROM chip also meant the PCM could be "retuned" if necessary to correct certain kinds of emissions or driveability problems. It also meant that if a bug was later discovered in the original factory programming, it could be corrected in the field by simply replacing the original PROM with an updated corrected PROM (a tactic GM has successfully used over the years to fix many factory flaws). Performance enthusiasts also liked replaceable PROMs because the chip could be replaced with o...