CC:
When I was first taught parasitic draw testing, it was very, very simple. You would take your meter, you either put it on the battery or put it in series measuring amps being drawn, close the door, and then if you had access to the fuse box, you would then start pulling fuses to see if the draw went away or went below specifications.
But on today’s vehicles, it is completely different. This is due to the fact that most vehicles have a power module that regulates the battery voltage, how the alternator works, and other things on the vehicle. It will switch off certain systems to conserve power, and it will even wake the vehicle up to perform certain functions. Let’s say it’s EVAP testing, or in the case of later model vehicles that have telematics functions, it will do updates on the vehicle. This can cause a draw on the battery that may be perceived as a parasitic draw, but it’s critical if you’re doing this type of testing. If you have a vehicle from a customer that’s sitting there and the battery dies overnight, you need to do this test.
But there’s different ways to do it. First of all, you can use a scope. This way, you can track when certain draws happen to the system. You can do your time division and make sure that those can capture a long period of time. But what you’re really looking at is when the vehicle goes to sleep and then wakes up. For this, you need a breakout box for the BD2. In here, you have different lights for the CAN bus and different circuits on the vehicle. This way, you can know what system is active and what’s gone to sleep. This way, you know that none of the modules are staying awake. Like let’s say for instance, you have an air ride problem. Let’s say an air sensor is miscalibrated or completely off. That module will keep the vehicle awake as it tries to trim the vehicle as it sits in some cases.
Also, the scope can catch other events that can cause a parasitic draw. Like let’s say for instance, you have a malfunctioning module that’s not communicating properly. It may have a U1000 code on it, and it’s causing other modules on the vehicle to stay awake and cause a draw on the battery that can kill it. By looking at these and using this box, you can know when it happens and you can help diagnose that problem. But here’s the top tip. If you’re using your scan tool during parasitic draw testing, you are going to get false results because the second you plug this in to the OBD circuit, it goes into a diagnostic testing mode, and some of the modules may not go to sleep. So when you’re doing parasitic draw testing, make sure you’re using the relevant tools for modern vehicles. I’m Andrew Markel. Thank you very much.
This video is sponsored by Auto Value and Bumper to Bumper.
