02 5.9 dually....check guage light came on and then disappeared after restart...but now the temp gauge doesn't functional well...140* is max temp recorded. I'm wondering how I check the voltage at the ECT sensor near the thermostat housing? PCU code 1682 ECU code 1693 using the OBD system. All other gauges work fine....just the temp gauge is down. Thanks

255K mileage...thermostat changed at 130K but maybe is stuck open??