contact us

How to Perform a Voltage Drop test

On Automotive DC Volt Systems

Voltage drop testing allows the technician to monitor voltage loss in a circuit. Voltage drop should be checked with the circuit loaded and a fully-charged battery.

In best case scenarios, voltage drop on a power side or ground side to a component through all connectors, and connections should not exceed 0.1V or 100mV, however most times 0.2V or 200Mv is acceptable. All voltage should be dropped across the load, not in the wires or connections supplying it power or ground.

In this video, we will show you how to test voltage drop on a starter motor circuit. This test can be applied to all components in a similar manner. Text instructions below video.


Set your digital volt ohm meter (DVOM) to read DC Volts.

Connect the negative lead of your DVOM to the positive terminal at the starter motor.

Connect the positive lead of your DVOM to the power source. In this case the positive battery terminal.

Operate the circuit to create the load. In this case we crank the engine.

Monitor the DVOM while cranking, he DVOM will display the difference in voltage between the two points.

If you find a voltage drop, move the negative lead to the next connector, connection or component in the circuit and run the test again. Changes in the Voltage Drop Reading indicate where excessive Voltage Drop is located.

We can test the negative side of the circuit in a similar manner.

Set your digital volt ohm meter (DVOM) to read DC Volts.

Connect the negative lead of your DVOM to the negative ground connection. In this case the negative battery terminal.

Connect the positive lead of your DVOM to the main engine ground.

Operate the circuit to create the load. In this case we crank the engine.

Monitor the DVOM while cranking, he DVOM will display the difference in voltage between the two points.

If you find a voltage drop, move the negative lead to the next connector, connection or component in the circuit and run the test again. Changes in the Voltage Drop Reading indicate where excessive Voltage Drop is located.