Have you ever noticed that your car battery seems to drain quickly, even when you’re not driving it? This could be a sign of a parasitic draw – a small but continuous flow of current that can drain your battery over time. Parasitic draws can be caused by a variety of factors, including faulty wiring, malfunctioning accessories, or even a parasitic battery.
To test for a parasitic draw, you’ll need a multimeter. A multimeter is a device that can measure voltage, current, and resistance. You can purchase a multimeter at most hardware stores. Once you have a multimeter, you can follow these steps to test for a parasitic draw:
Identifying Electrical Components
Before performing a parasitic draw test, it’s crucial to familiarize yourself with the electrical components in your vehicle. These components may include:
- Battery: Stores electrical energy and provides power to the vehicle.
- Alternator: Charges the battery while the engine is running.
- Starter: Engages the engine by turning the crankshaft.
- Fuses: Protect electrical circuits from excessive current.
- Relays: Control the flow of electricity to different components.
- Wiring: Connects electrical components and allows current to flow.
Thoroughly understanding the function and location of these components will help you effectively identify and troubleshoot potential sources of parasitic draw.
| Component | Function | Location |
|---|---|---|
| Battery | Stores electrical energy | Typically located under the hood |
| Alternator | Charges the battery | Usually mounted on the engine |
| Starter | Engages the engine | Connected to the flywheel |
Isolating Individual Circuits
With the battery disconnected, begin by isolating individual circuits. To do this, remove the fuses or circuit breakers one at a time and test for current draw.
Step 1: Disconnect the negative battery terminal and wait for the parasitic draw to settle.
Step 2: Start by removing the fuse or circuit breaker that protects the circuit you suspect may be causing the parasitic draw.
Step 3: Reconnect the negative battery terminal and check the ammeter reading. If the current draw decreases significantly, then the circuit you removed the fuse or circuit breaker from is likely the culprit.
Step 4: Repeat this process for each circuit until you have identified the one causing the parasitic draw.
Note: Some parasitic draw is normal, so do not be alarmed if you still see a small amount of current draw after isolating all the circuits. The acceptable level of parasitic draw will vary depending on the vehicle, but it is typically in the range of 0.02 to 0.05 amps.
Using an Ammeter to Measure Current Draw
An ammeter is a device that measures current flow. To use an ammeter to measure parasitic draw, follow these steps:
Step 1: Set the ammeter to the appropriate range. For most vehicles, a range of 10 amps or less will be sufficient.
Step 2: Connect the ammeter in series with the negative battery terminal. To do this, disconnect the negative battery terminal and connect one lead of the ammeter to the battery terminal. Then, connect the other lead of the ammeter to the negative battery cable.
Step 3: Record the current draw reading. The reading will be in amps.
Verifying the Results
After completing the parasitic draw test, verify the results to confirm the presence and extent of the parasitic draw. Here are the steps for verifying the results:
- Disconnect the vehicle’s negative battery terminal: Ensure the engine is off and the key is out of the ignition. Disconnect the negative battery terminal using a wrench.
- Install an ammeter in series: Use an ammeter with a range of at least 10 amps. Connect the positive lead of the ammeter to the disconnected negative battery terminal and the negative lead to the battery post.
- Wait for the parasitic draw to stabilize: Allow the vehicle to sit for at least 30 minutes, allowing the modules to go into sleep mode and the parasitic draw to settle.
- Read the ammeter: Record the ammeter reading. A reading of less than 50 milliamps (mA) is considered normal, while readings above 100 mA indicate a parasitic draw.
- Check for a temperature dependence: If the parasitic draw is suspected to be temperature-dependent, repeat the test at different ambient temperatures to observe any variations.
- Repeat the test multiple times: Conduct the parasitic draw test several times to confirm the consistency of the results. Multiple tests help eliminate any potential measurement errors.
- Compare the results to specification: Refer to the vehicle’s service manual or consult with a certified technician to determine the acceptable parasitic draw range for the specific make and model.
- Inspect for obvious sources: Visually inspect the vehicle for any obvious sources of parasitic draw, such as loose wires, damaged components, or aftermarket accessories.
- Isolate the circuits: Use the ammeter to isolate the circuits by disconnecting individual fuses or relays and monitoring the ammeter reading for changes.
- Test each circuit individually: Once the circuit with the parasitic draw is identified, test each component within the circuit using the ammeter to pinpoint the exact source of the draw.
How to Test for Parasitic Draw
A "parasitic draw" occurs when an electrical device or component in your vehicle continues to draw power even when the ignition is turned off. This can lead to a drained battery and difficulty starting your car.
Testing for a Parasitic Draw
To test for a parasitic draw, you will need a multimeter.
Step 1: Prepare Your Vehicle
- Turn off the engine and remove the keys from the ignition.
- Open the hood and locate the negative battery terminal.
- Disconnect the negative battery cable using a wrench or socket wrench.
Step 2: Connect the Multimeter
- Set the multimeter to the DC amps setting, typically 10 or 20 amps.
- Connect the red positive lead of the multimeter to the negative battery terminal.
- Connect the black negative lead of the multimeter to the negative battery cable.
Step 3: Check for a Draw
- Wait a few minutes. The multimeter should read a value below 50 milliamps (mA).
- If the multimeter reads a higher value, there is a parasitic draw.
- To identify the source of the draw, start pulling fuses one by one.
- When you pull the fuse that stops the draw, the multimeter reading will drop significantly. The device or component associated with that fuse is the source of the parasitic draw.
People Also Ask About How to Test for Parasitic Draw
What is a normal parasitic draw?
A normal parasitic draw is typically less than 50 milliamps (mA).
How long can a car battery last with a parasitic draw?
The length of time a car battery can last with a parasitic draw depends on the size of the battery and the magnitude of the draw. A small draw may not affect the battery for months, while a large draw could drain the battery in a few days.
What are some common sources of parasitic draw?
Common sources of parasitic draw include:
- Interior lights
- Trunk lights
- Power outlets
- Security systems
- Faulty electrical components
