About to fit an AFR gauge

Checked the wiring on the 93 WRX and found the following,
Three wires, one reading the 12v feed, the other the earth. these were fine. But the signal wire reads 5 volts

It sould go to a max of around 1 volt. Correct?

So the gauge reads rich all the time.

Should I assume that the probe is shot then?

Thanks

P.s the probe is in the up pipe . The headers have been changed for a set of semis. Cant see this changing anything.

Car has also had d pipe , fuel pump fitted at the same time