Volt drop testing is a valuable diagnostic procedure, which is often overlooked.
Volt drop refers to the potential difference in a direct circuit. That is the difference between the voltage at point ‘a’ and the voltage at point ‘b’.
In this instance, we are looking at the voltage difference between the battery negative terminal and the engine block. That means we are checking the circuit integrity of the negative or ground cable, including any connections, and its connection status with the engine block, which usually represents the ground circuit for the starter motor.
Volt drop testing requires current to be flowing and so when looking at the ground circuit we need to load it fully. This is true of all volt drop tests.
In this case, loading the circuit fully means operating the starter motor.
Check out this brief video to see how I perform such a test.
Battery Volt Drop Test: https://youtu.be/o2Nx0z97ZGM