Test purpose:This test is designed to monitor the resistance value of the thermistor and determine if itis within range of the operating specifications. Thermistors are either NTC or PTC typeand their resistance values are variable depending on the temperature that they aresensing. A thermistor can either be open, shorted or operating correctly or incorrectly. Inthis test we are looking to determine if the resistance change in the thermistor is smoothand consistent over the increase and decrease in temperature. Although this test is nota definitive “pass / fail” or “green light / red light” the tool is automatically set up for afast resistance capture with stable readings and ranged correctly. Once connected to athermistor, the graphing screen will be the way to monitor output.Tool Setup:• Top Chanel: N/A• Bottom Channel: Resistance - Ranged to 10MΩ• Set Min/Max to Max• Speed: 64MS (256) or (4000 Hz 256 SMPL)Test Procedures:• Place Leads on tool to Ohms and Common• Use Probe Tips on leads or clamps• Remove the thermistor from a power source.• Connect the positive probe tip or clamp to the positive output of thethermistor• Connector the ground probe tip or clamp to the ground of the thermistor• Look for “out of range” , a “stuck” Ω value or a slightly fluctuating μΩreading.• Set the Meter Mode to Graph• Begin to heat up the thermistor.• Watch the characteristics of the reading for a gradual change in theresistance or Ω reading.RecommendationsA thermistor is not actively powering itself, but rather creating a voltage drop acrossitself based on temperature. A faulty thermistor reading on the vehicle may be thecause of the thermistor, the thermistor circuit, or the computer monitoring thethermistor value.Diagnosis of a thermistor should be broken into the 3 categories of component,circuit and computer.Diagnosing the thermistor:• A thermistor can either be open, shorted, operating correctly or incorrectly.• If the thermistor is open, the reading will be “out of range” or a the tool will seefluctuating resistance values due to ghost voltage (a fluctuation of voltagerandomly from the air and other electronics around us).• If the thermistor is shorted it will either see an Ohms value on the screen thatfluctuates but does not intentionally increase or decrease or at least an ohmsvalue reading that does not change due to the nature of how ohmmeters work.• If the thermistor is operating incorrectly, the changes in its internal resistancevalues will change sharply as consistent temperature is applied to the elementand the readings will appear to “jump” or “drop”significantly as element is beingheated and monitored.Diagnosing the circuit:If the thermistor is found to be operational or operating as expected but the issuestill exists the next step is to diagnose the thermistor circuit.• Begin with the connectors, then the feeds or cables and end with the grounds.• Visually inspect and wiggle test the circuits.• Use the “loaded cable” or “cable tests” from the voltage drop menu to verify thereis no undue voltage drop on the system. (If possible and safe a loaded test of thecables disconnected from any computer circuits would be preferable.)• If the problem still exists, attempt to diagnose the monitoring system of thethermistor using a wiring diagram to identify what is monitoring the thermistorvalue.