Discovering a parasitic draw on your vehicle’s electrical system can be a frustrating and time-consuming task. A parasitic draw is a small amount of electrical current that continues to flow from your car battery even when the engine is turned off and all accessories are turned off. This can lead to a dead battery and leave you stranded. Use the guide below to help you check for a parasitic draw in your vehicle’s electrical system.
To start, you’ll need a multimeter. This is a small, handheld device that measures electrical current. You can find one at most hardware stores or online. Once you have your multimeter, you’ll need to set it to the DC volts setting. Then, you’ll need to connect the positive lead of the multimeter to the positive terminal of your car battery. Connect the negative lead of the multimeter to the negative terminal of your car battery.
Now, you’ll need to turn off your engine and all accessories. Wait a few minutes for the electrical system to settle down. Then, take a reading on the multimeter. The reading should be close to zero. If it’s not, then you have a parasitic draw. To find the source of the parasitic draw, you’ll need to start pulling fuses one at a time until the reading on the multimeter drops to zero. The fuse that causes the reading to drop is the circuit that’s causing the parasitic draw.
Gather the Necessary Tools
To check for a parasitic draw, you will need the following tools:
- A multimeter
- A pair of jumper wires
- A 12-volt battery charger
Multimeter
A multimeter is a device that measures electrical current, voltage, and resistance.
When checking for a parasitic draw, you will use the multimeter to measure the current draw from the battery.
It is important to use a multimeter that is capable of measuring low currents, as parasitic draws are typically very small.
| Multimeter Range | Parasitic Draw Measurement |
|---|---|
| 10 milliamps (mA) | Most common range for parasitic draw testing |
| 1 milliamp (mA) | For very small parasitic draws |
| 100 microamps (µA) | For extremely small parasitic draws (rare) |
When selecting a multimeter, it is also important to consider the accuracy and resolution of the device.
A more accurate and higher-resolution multimeter will provide more precise measurements.
Inspect Electrical Components and Wiring
Isolating the Affected Circuit
- Disconnect the negative battery terminal to isolate the electrical system from the battery.
- Connect an ammeter between the negative battery terminal and the disconnected cable.
- Set the ammeter to measure current in milliamps or microamps.
- Begin removing fuses one at a time, starting with the ones that control non-essential accessories like power windows and radios.
Identifying the Parasitic Circuit
- Monitor the ammeter as you remove each fuse. When the ammeter reading drops significantly or goes to zero, you have identified the circuit with the parasitic draw.
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Tracing the Parasitic Draw
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Inspecting Relays and Solenoids:
- Relays are electromechanical switches controlled by an electrical signal. They can become stuck or fail, causing a constant current draw.
- Solenoids are electrical actuators that convert electrical energy into mechanical movement. They can also fail, leading to parasitic draw.
- Check for any relays or solenoids that are staying engaged or activated after the ignition is turned off.
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Examining Electronically Controlled Modules (ECMs):
- ECMs control various electrical functions in the vehicle. A faulty ECM can cause unexpected electrical loads or malfunctions.
- Check for any ECMs that are overheating, showing signs of damage, or have loose or corroded connections.
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Identifying Failed Diodes and Rectifiers:
- Diodes allow current to flow in one direction and block it in the other. Faulty diodes can create a parasitic current path.
- Rectifiers convert alternating current (AC) to direct current (DC). A failed rectifier can cause current to flow in the wrong direction, leading to parasitic draw.
- Check for any diodes or rectifiers that are overheating, showing signs of damage, or have loose or corroded connections.
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Looking for Short Circuits:
- Short circuits occur when two wires or components come into contact, creating a low-resistance path for current to flow.
- Inspect the vehicle’s electrical system for any exposed wires, damaged insulation, or loose connections that could cause a short circuit.
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Checking for Ground Faults:
- Ground faults occur when an electrical component is not properly grounded to the chassis. This can allow current to flow through the vehicle’s body, creating a parasitic draw.
- Inspect the vehicle’s grounding points for any loose connections, corrosion, or damage.
Reassemble the Vehicle
Once you’ve located the parasitic draw, it’s time to reassemble the vehicle. Here’s how to do it:
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Disconnect the negative battery terminal.
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Remove the fuse or relay that you identified as the source of the parasitic draw.
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Reconnect the negative battery terminal.
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Start the vehicle and let it run for a few minutes.
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Use a multimeter to measure the current draw from the battery.
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The current draw should now be below 50 milliamps.
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If the current draw is still above 50 milliamps, there may be another source of parasitic draw.
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Repeat steps 2-7 until the parasitic draw is eliminated.
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Once the parasitic draw has been eliminated, replace the fuse or relay that you removed.
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Test the vehicle to make sure that everything is working properly.
Tips for Reassembling the Vehicle
Here are a few tips for reassembling the vehicle:
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Make sure that all of the electrical connections are tight.
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Replace any damaged fuses or relays.
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Clean the battery terminals and cables.
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Test the vehicle’s electrical system before driving it.
How to Check for a Parasitic Draw
A parasitic draw is a condition in which an electrical device or circuit continues to draw power from the vehicle’s battery even when the vehicle is turned off. This can lead to a drained battery and prevent the vehicle from starting. There are a few simple steps you can take to check for a parasitic draw:
1. Disconnect the negative battery terminal.
2. Connect a multimeter in series between the negative battery terminal and the battery.
3. Set the multimeter to the DC amps scale.
4. Wait for a few minutes to allow the multimeter to stabilize.
5. The multimeter should read a current draw of less than 50 milliamps. If the current draw is higher than 50 milliamps, there is a parasitic draw.
People Also Ask About How to Check for a Parasitic Draw
What are the symptoms of a parasitic draw?
The symptoms of a parasitic draw can include:
- A drained battery
- Difficulty starting the vehicle
- Dim headlights
- Electrical components that do not work properly
What are the causes of a parasitic draw?
The causes of a parasitic draw can include:
- A faulty alternator
- A faulty starter
- A faulty electrical component, such as a light bulb or a radio
- A damaged wire
How can I fix a parasitic draw?
To fix a parasitic draw, you will need to find the source of the draw and repair or replace the faulty component. Here are a few tips for finding the source of a parasitic draw:
- Start by disconnecting the negative battery terminal.
- Then, use a multimeter to test the current draw of each electrical component.
- The component with the highest current draw is the most likely source of the parasitic draw.
- Once you have found the source of the parasitic draw, you can repair or replace the faulty component.
