Using An Analog Meter for TPS Sensors

Now that the digital multimeter and storage ‘scope have taken over electrical troubleshooting, you’ve probably buried that old analog meter in the bottom of the box, right? Maybe there’s life in the old needle-and-scale meter yet, especially when you’re searching for elusive intermittent failures. An example is conventional style throttle position sensors. They operate like the volume control on a radio, as a variable resistor or potentiometer, changing resistance with the rotation of the throttle shaft. One failure mode leaves a “dead spot” across the arc of the sensor’s wiper where it contacts the resistance element. There are two sensor-side ways to test TPS units. One is by disconnecting the harness, and checking for variable resistance using the ohms function of a multimeter. The other is to test the system live and look for an output voltage that varies with throttle position. Digital multimeters have all but taken over general electrical testing, but the number can bounce like a slot machine until they stabilize, leaving a poor picture of the sensor’s action. Use an analog meter, however, and the needle will respond with a sudden dive downwards, (dead spot) or upwards (short). It will likely appear as a brief “blip” that repeats as you wind the throttle shaft back and forth past the affected area. It’s a fast, cheap test that leaves you with “go-no-go” certainty about the TPS.