False temperature - Dodge Neon

Have a 2000 Dodge Neon with 84,000. Because I live close to work, it is driven 4-5 times week (low miles). Recently, the temperature gauge did not move, then jumps to hot, then back to low. On occasion, it goes to the correct temperature. My mechanic ran diagnostics and pressure check. Pressure check was okay. Diagnostic showed something, but when that part was replaced, the problem continued so the old part was put back in. Any suggestions?

It would help us if you told us the part he replaced, then removed. If it was not the temperature sending unit, then that’s the part you need to replace now.

ECT sensor was replaced.

Don’t remember which car it was, but had the same problem. New thermostat fixed it.

The wiring diagrams from the ARRC (Auto Repair Reference Center) web site (through the local public library) shows a violet/yellow wire from the temperature gage to the #59 terminal, called the PCI bus, on the PCM (Powertrain Control Module), aka engine computer. Power to the gage comes from a fuse on a dark blue/white wire. There could be a problem in either wire, or, their terminals.