OBD1 testing unable to pull codes?

On my RV I have tried pulling codes. Can’t seem to get any with every method I’ve tried. Wire jumping, test light, and even the tool won’t work.
Check engine light stays on constantly, and I have tried disconnecting the battery and PCM to reset. The light was still on when I hooked it back up. Any suggestions? Could my single pin test wire be short/ground? Please help.