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Testing Parasitic Draw via Fuse Voltage Drop

Using This Method Prevents the Vehicle From Waking During Testing

A parasitic draw test is required when a vehicle battery becomes discharged with the key in the off position. A component or components are drawing current from the battery when they should not be. This test will show you how to quickly pinpoint the source of the draw using voltage drop across fuses. This method is fast and efficient in comparison to monitoring current and removing fuses. Using this method prevents the vehicle from waking up during the test, causing you to have to start over from sleep mode.

 

 

Text instructions below video:

Begin by gaining access to the fuse panels to prepare for testing. 

Then close all door latches and place the hood pin switch in the closed position. This will begin the vehicle sleep process. After an hour the vehicle should be asleep or completely shut down. Some vehicles take up to two hours.

Using a low amp clamp and a digital volt ohm meter (DVOM), confirm there is a parasitic draw. Note the amount of draw you find.

Our subject vehicle has a parasitic draw of 60 milliamps. This is enough to discharge the battery.

With our confirmed fault, we head to the interior fuse panel to pinpoint the source of the draw.
Set your DVOM to read millivolts.

Place the positive and negative test probe on each side of a single fuse. 
Record the absolute voltage value. Ignore negative voltage readings or switch your test probe orientation if seeing the negative symbol distracts you. Record the amount of voltage drop present.

Check all fuses to be sure you located each circuit causing the parasitic draw. Our vehicle has a confirmed 6 millivolt voltage drop across a single fuse. Record that amount.

Next, reference the chart to calculate the amount of milliamp draw. The chart confirms we have 60 milliamps on a single circuit.

Next, use a wiring diagram to identify the component causing the draw. In our subject vehicle, the seat heater relay was causing the draw.