A high voltage fault normally occurs because the ECU doesn't see a voltage drop across the sensor. This could be caused by a disconnected sensor, or the sensor may be faulty; you might also have a faulty ground wire. Download your service manual from sea doo manuals.net, and go to the last few pages (schematics). Find out which wires go to the external temp sensor (probably a 2 wire sensor), and disconnect it from the sensor. One wire should have 12 vdc (that's the power wire), the other wire should have < 200 mv. If you see 12 VDC on the power wire and 0 volts on the ground; replace the sensor.