Temp gauge goes to red before start up.

2001 1500 5.9l
Got a cel for temp over range an check gauge light. The temp gauge will go to the max in red with the key in the on position an stays there even when started up. It will go back but once power is off.

I got a new temp sensor an still have the same thing going on.
This is the last thing i need to get fixed before i can get it tagged an on the road again.

Anyone have any input?

I would test the temperature sensor wiring at this point. I doubt the IC has gone bad.

You will need a multimeter.
On the temp sensor connector, there are two wires, black/light blue and tan/black.
With your multimeter set to reading voltage, probe from battery ground to the tan/black wire, you should read 5volts. If not, set the multimeter to resistance and probe from battery ground to the tan/black wire, if it indicated a low value of resistance, the wire is shorted to ground, if it indicated OL or a very high value, the wire is broken open.

If the tan/black wire reads 5volts, probe from battery ground to the black/light blue wire on the voltage setting. You should read very close to 0volts. If that is good, switch to resistance and repeat the measurement, you should see near 0 ohms. If the reading is OL, the sensor ground wire is broken open and needs to be repaired (just running a new wire to ground is not sufficient, the sensor ground must be run through the proper PCM pin)


I wish I could tell you which situation is more likely, a short to ground on the 5v side, or an open circuit, but I cant find anywhere saying if these are PTC or NTC thermistors.

+1 to likely bad ground.