How to Check Amp Draw on a Car

Title: How to Check Amp Draw on a Car: A Comprehensive Guide


Understanding the amp draw of your car’s electrical system is crucial for diagnosing potential issues and ensuring its optimal performance. Whether you suspect a battery drain or simply want to monitor your vehicle’s electrical health, knowing how to check amp draw on a car is a valuable skill. In this article, we will walk you through the process step step and address some common questions related to amp draw measurements.

How to Check Amp Draw on a Car:

Step 1: Gather the necessary tools and equipment. You will need a digital multimeter capable of measuring amps, a wrench or socket set, and safety gloves.

Step 2: Ensure that your car is in a safe environment and turned off completely. Open the hood and locate the battery.

Step 3: Disconnect the negative terminal of the battery using the wrench or socket set. This step is crucial for preventing any accidental electrical shocks.

Step 4: Set your multimeter to the ampere (A) setting and connect the meter’s leads in series with the negative battery cable and the negative battery post.

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Step 5: Turn on the multimeter and observe the reading. If there is no significant draw, the reading should be close to zero. If there is a draw, the multimeter will display the amperage being drawn from the battery.

Step 6: Begin troubleshooting removing and replacing one fuse at a time from the fuse box. Each time a fuse is removed, check the multimeter reading to see if the draw decreases. This will help identify the circuit responsible for the excessive amp draw.

Step 7: Once the problematic circuit is identified, consult your car’s manual or seek professional assistance to diagnose and repair the issue.

Common Questions and Answers:

1. How much amp draw is considered normal?
– A typical amp draw for a vehicle at rest should be less than 50 milliamps (mA). Any reading above that indicates a potential issue.

2. What causes excessive amp draw?
– Common causes include faulty electrical components, short circuits, malfunctioning switches, or a parasitic drain from aftermarket installations.

3. Can a dead battery cause excessive amp draw?
– No, a dead battery is a result of excessive amp draw, not the cause.

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4. How often should I check the amp draw on my car?
– It is recommended to check the amp draw whenever you suspect a battery drain or as a preventative measure during routine maintenance.

5. Can a bad alternator cause excessive amp draw?
– No, a bad alternator can cause charging issues, but not excessive amp draw.

6. How long should I wait after turning off the car to check the amp draw?
– Wait at least 15-20 minutes to allow the car’s systems to enter a sleep mode before checking the amp draw.

7. Can a faulty battery charger cause excessive amp draw?
– Yes, a malfunctioning battery charger can draw excessive amps, which can damage the battery and other electrical components.

8. Is it safe to check the amp draw on my car’s electrical system myself?
– As long as you follow safety precautions and have a basic understanding of electrical systems, it is safe to perform this procedure.

9. Should I disconnect the positive or negative terminal of the battery when checking amp draw?
– Always disconnect the negative terminal to avoid potential short circuits.

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10. Can a failing starter cause excessive amp draw?
– Yes, a failing starter could draw excessive amps, leading to battery drain.

11. Can a faulty alternator cause a high amp draw?
– A faulty alternator can cause an excessive amp draw if its internal diodes fail.

12. Is it necessary to replace a fuse if it shows excessive amp draw?
– Yes, a fuse showing excessive amp draw is a clear sign of a problem and should be replaced.

13. Can extreme weather conditions affect amp draw readings?
– Yes, extremely cold temperatures can cause higher amp draw due to increased resistance in electrical components.


Checking the amp draw on a car is a valuable skill that enables you to identify and resolve potential electrical issues. By following the step--step guide provided in this article, you can diagnose excessive amp draw and take appropriate measures to maintain your car’s electrical system. Always prioritize safety and seek professional help if you are unsure about any aspect of the process.

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