Disonnect the wire from the sensor and touch it to a grounded metal part of the engine (with ignition on). If the guage then goes to hot then sensor is faulty. If not then wiring or guage is faulty.
Presumably all the other guages and warning lights are OK, if not check fuses first.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)