Test purpose:The 3 wire Ω test is designed to identify if a potentiometer is operating correctly or at leastbehaving in a normal manner. Because there are many behaviors of a potentiometer valuethat can be monitored this test will not provide a “green light / red light” or “pass / fail” butit will allow you to monitor the behavior of the sensor and determine if it is behaving as itshould in it’s given application. It is important to note that the resistance values of thepotentiometer can value greatly from make, model and purpose so the auto rangefunctionality must be left on. Three Wire potentiometer or position sensors will have areference voltage pin, ground pin and output pin. In a 3 wire potentiometer sensor theoutput pin or signal reference pin is providing a voltage reading proportional to themovement of the system being monitored by the sensor typically within a 5 volt range(typically 0 - 5 volts). The output pin is effectively a voltmeter and provides a voltagereading based on the physical movement of the arm internally that is touching the resistorthat is powered by the reference voltage and providing an output voltage value based onwhere the physical position of that arm is. In an off vehicle test, the potentiometer will actas a rheostat when no voltage reference is provided or present and produce a variableresistance value.Tool Setup:• Top Chanel: N/A• Bottom Channel: Voltage DC - Auto Ranged• Speed: 64MS (256) or (4000 Hz 256 SMPL)Test Procedures (on vehicle or powered with 5V ref):• Place Leads on tool to Volts DC and Common• Use Probe Tips on leads or clamps• Connect the positive probe tip or clamp to the positive output of thepotentiometer• Connector the ground probe tip or clamp to the ground of the potentiometer• Look for stuck voltage reading, 0 voltage reading or a fluctuating μV (microvolt)reading.• Set the Meter Mode to Graph• Begin to move the shaft (or component), blade, arm or crank being measured (orcomponent)• Watch the characteristics of the reading for a proportional change in the voltageor V to the movement you are creating.RecommendationsA potentiometer is actively powered by a 5V reference. Internally the resistor is consuming voltagerelative to the position of the arm being moved. Depending on the position of the arm the resistorcan consume all of the voltage, none of the voltage or somewhere in between. The output of thevoltage value is proportional and relative to the position of the arm on the resistor. In apotentiometer resistance value check, the potentiometer must be removed from the power sourceand a voltage drop across itself is created based on location of the sensing arm on the resistor. Afaulty potentiometer or position reading on the vehicle may be the cause of the sensor, the sensorcircuit (ground, Vref or output), or the computer monitoring the sensor value.Diagnosis of a potentiometer should be broken into the 4 categories of sensor, circuit, computerand Component being “sensed” or monitored by the sensor.Diagnosing the sensor:• A potentiometer can either be open, shorted, operating correctly or incorrectly.• If the potentiometer is open, the reading will be “0 Volts” or the tool will see fluctuating voltagevalues due to ghost voltage. If no reference voltage is present this will also occur. If the resistorinside is open the Vref pin and Ground pin will show “0 Volts” or ghost voltage. If the sensingarm and ground are open the output pin and ground will show “0 Volts” or ghost voltage.• If the potentiometer is shorted on the ground pin and output voltage pin it will either see 0 Voltsvalue or a stuck voltage value.• If the potentiometer is operable, but operating incorrectly, the changes in its internal resistancevalues will change sharply as movement is applied to the component and the readings willappear to “jump” or “drop”significantly as sensor arm or blade is moved.Diagnosing the circuit:If the potentiometer is found to be operational or operating as expected but the issue still existsthe next step is to diagnose the potentiometer circuit.• Confirm Reference Voltage and Ground are present.• 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 there is no unduevoltage drop on the system. (If possible and safe use a loaded test of the cables disconnectedfrom any computer or srs circuits.)Diagnosing the component being monitored:• After confirming the potentiometer has good reference voltage and ground, monitor the outputvoltage and activate or manually engage the position component being monitored to confirmthe component is operating as expected. If operating as expected diagnose the monitoringsystem.