Getting behind the wheel only to find your car’s battery is dead is inconvenient the first time it happens. When it happens again, it’s time to consider the possibility of a slow battery drain, also known as a parasitic draw. While aftermarket accessories are often blamed for these bothersome issues, not all parasitic draws are so simple to diagnose.
The guide below provides step-by-step instructions for testing for parasitic draws with a multimeter. We’ll also review the common culprits behind parasitic draws and offer tips on how to resolve them quickly. Rely on Identifix Direct-Hit’s comprehensive database—complete with full-color, interactive wiring diagrams—to help you efficiently locate and address parasitic draws and any other electrical issues.
Electrical gremlins cause mechanics no end of grief. However, it’s important to keep yourself safe when diagnosing these types of issues. Ensure the vehicle you’re working on is off and that you wear the appropriate safety gear—such as gloves and eye protection—to minimize any potential problems.
To complete the parasitic draw test successfully, you’ll need the following tools:
Testing for parasitic drw with a multimeter may call for additional tools like clamps, wedges, or jumper clips. The use of these tools varies by make, model, and model year.
For the most accurate fixes possible and detailed tool recommendations for make, model, and year, check out our Direct-Hit database, backed by expert-verified solutions.
1. Rule Out the Charging System
Before you dig out your digital multimeter or start pulling fuses, begin by ruling out the cause of your dead battery by the process of elimination. Ensure the battery, alternator, and starter function properly. If you encounter any problems with these components, address them and monitor your vehicle to determine if the symptoms persist.
2. Check for Trouble Codes
After checking your battery, starter, and alternator off the list, review any pending trouble codes your vehicle might be storing. Certain makes and models will alert drivers to a parasitic draw by throwing a code. Should you find any pending codes, address them before moving on to the next step.
3. Perform a Road Test
It’s best to do this road test with a partner, as you’ll need to verify the various components inside the vehicle function properly. This step requires pushing a lot of buttons and testing out the various features of your vehicle. Note any accessories that don’t perform as expected.
4. Initiate the Vehicle’s Sleep State
Once the road test is complete, open the doors, trunk, and hood, ensuring the latches are tripped to trick the engine control module (ECM) into thinking the vehicle is closed up and secure. With nearly unlimited access to the interior, you can begin your parasitic draw testing. Set the keys far enough away from the car that it won’t attempt to communicate with the fob as you test.
5. Run the Digital Multimeter in Series
Before you let your vehicle go into a relatively dormant state, you need to place your digital multimeter in the circuit between the battery and the rest of the car. Be especially cautious during this step, as drawing more than 10 amps can pop the circuit in your multimeter. Set your multimeter to auto-range if equipped or milliamps if not.
Disconnect the battery negative cable and connect it to the multimeter’s positive (red) lead. Place the negative (black) lead on the battery negative terminal. Now your multimeter will read any amperage flowing out of the battery.
6. Wait Until the Vehicle’s Systems are Dormant
Many of your vehicle’s systems shut down once you turn off the engine, but not everything goes to sleep immediately. Give your vehicle some time to enter sleep mode. Some cars require a few minutes or less, while others may require up to an hour or more.
7. Verify Parasitic Draw
After most of the systems in your vehicle have gone dormant, monitor the amperage reading on your multimeter. It will pick up any remaining draw on the battery. Readings of less than 50 milliamps are acceptable and normal for most vehicles, but it depends on the make and model. If your multimeter reads more than 50 milliamps, a parasitic draw exists.
8. Locate the Fuse Box
Your vehicle may have one or more fuse boxes in multiple locations. Most fuse boxes are located beneath the hood (near the battery), near the driver’s side door, or beneath the dash on the passenger’s side. Consult your owner’s manual for exact fuse box locations.
9. Test for the Parasitic Draw Source
With a second digital multimeter set to millivolts, test the metal tabs of the fuses in each fuse box. Place the leads on the metal tabs and monitor the resulting reading. Anything higher than a zero millivolt reading indicates a flowing current.
10. Trace the Faulty Fuse
When you’ve located a fuse that reads higher than zero millivolts, use the wiring schematic for that fuse box or your owner’s manual to determine which circuit it ties into. Avoid removing the fuse. Should the fuse power multiple components, disconnect them one at a time to further locate the source of the parasitic draw.
11. Determine Next Steps
Determining which fuse is responsible for the parasitic draw is only the first part of this multi-step diagnostic process. Next, you’re faced with a choice of either fixing the faulty component or leaving the fuse unplugged. In some cases, the lack of a fuse may not interfere with normal vehicle operations, but that’s not always the case.
12. Repeat Parasitic Draw Tests to Confirm Fix
If you opt to fix the faulty component causing the parasitic draw, perform this test once more to ensure the problem has been adequately addressed. Remember, the baseline draw on your car’s battery shouldn’t exceed 50 milliamps, depending on your vehicle’s make and model. Proper battery care and maintenance can also help you avoid walking out to a dead battery.
The Innova 3320 and 3340 digital auto-ranging multimeters are two of the most common digital multimeters available to DIYers and professional mechanics. The Innova 3320 multimeter is inexpensive and comes with basic features like a built-in stand, auto shut-off, and rubber corner guards. It’s a handy addition to any DIYer’s toolbox.
| Ranges | Innova 3320 | Innova 3340 |
| AC/DC Volts (volts) | 0–600 | 0–600 |
| Resistance (megaohms) | 0–20 | 0–40 |
| DC Amps (amps) | 0–10 | 0–15 |
| AC Amps (milliamps) | 2–100 | 0–100 |
| Diode Test (volts) | 0–2 | 0–2 |
| Continuity Test (ohms) | 0–200 | 0–200 |
In contrast, the Innova 3340 incorporates advanced features catered to professional mechanics, including a temperature probe, min/max and hold functions, and an inductive clamp. Well-suited to industrial settings, this robust multimeter allows you to save data for later reference. The Innova 3340 also offers a higher level of precision than the more basic 3320 multimeter.
Running a parasitic draw test with multimeters enhances and highlights the challenges that mechanics face when diagnosing electrical issues in vehicles. Identifix Direct-Hit streamlines these processes with comprehensive, vehicle-specific diagnostic and repair data that boosts efficiency and productivity. Contact us to speak with a friendly and knowledgeable representative about the Identifix suite of auto repair shop software solutions and services.
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