There are scan tools that can access the OBDI vehicles, for example I have an older SnapOn MT2500 that has cables for the two connectors on the OBDI Chrysler vehicles. The problem is OBDI was not standardized so a tool for those vehicles had a more limited market (or was very complex if it covered many vehicles) so cost was higher.
OBDII was pretty comprehensive even in 1996, but not everything sets a code even if there is a stall.
OBDII was pretty comprehensive even in 1996, but not everything sets a code even if there is a stall.