Ask the Expert: My Power Probe is reading voltage fine, but there are no lights or tones. Why?

Feb. 27, 2016
Good news! There is nothing wrong with your Power Probe.

Q: My Power Probe is reading voltage fine, but there are no lights or tones. Why?

A: Power Probe Circuit Testers have red and green LED indicators and distinct audio tones that tell you if you are probing on the power side or ground side of circuit. When testing with your Power Probe, you may have encountered a situation where the display is reading voltage correctly but the LED indicators and tones are not activating. Good news! There is nothing wrong with your Power Probe. This is actually a normal condition we call “Automatic Voltage Drop Detection,” and it is the probe's way of alerting you that there is too much voltage loss in the circuit.

Let me explain... Power Probe Circuit Testers are always connected to and powered by the vehicle’s battery. Because of this permanent connection, they are always comparing the voltage measured at the probe tip to the voltage from the source battery and looking for any loss in voltage or “voltage drop” in the circuit. The general rule of thumb for a 12VDC electrical system is no more than 0.5V of total voltage drop from the battery to the load.

The Power Probe III, Power Probe IV, and the Power Probe Hook all have built in LED and tone indicators that will always light up as long as the tip voltage is within 0.5V of the battery voltage that the probe is connected to. If voltage difference between the battery and the tip is greater than 0.5V, the LEDs won’t light and the tone will not sound, instantly alerting you that the circuit has excess voltage drop.

This makes voltage drop testing with a Power Probe effortless and automatic.

Information provided by: Power Probe

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