The sending units on these are simply an NTC (negative temperature
coefficient) thermistor. They are cheap enough that the easiest way
to eliminate the sender is just to try a replacement. Or you can
check the sender's resistance at a kniown temperature. If you want,
you can substitute various resistance values for the sender to see if
the wiring/PCM are OK. Some examples:
177 Ohms = 212 F
973 Ohms = 122 F
3520 Ohms = 68 F
(values are not exact, +/- 10 percent is fine)
my quick test is:
Remove wiring and ground it.
If the gage pegs hot, it's good. Plug the wires back in.
Next measure the temp near the sensor (I use a Raytek infrared digital
thermometer). If the temp is 200 and the gage says 100, replace sensor.
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