Door Ajar Switch Car Can Drain Battery [The Correlation Is Real!]

Did you accidentally leave the car’s door open last night, and now the battery’s dead? Sorry to break it to you, but the likeliest culprit here is the door ajar warning light.

In most cars, the door ajar sensor is a ‘Caution Light’ on the dashboard. If any of your car’s doors aren’t completely shut, this light will come on. As soon as you’ve shut them all, it will go off.

A door ajar sensor’s primary function is to detect and send a signal to the Electronic Control Unit (ECU) if any door is left open, marginally or entirely.

When a door is not fully closed, a warning icon on the dash will illuminate to remind the driver. But does leaving a car door ajar actually cause the battery to drain completely?

The battery in your automobile can die if the door ajar light stays on, which can occur for a wide range of reasons depending on the make and model of your car.

Before you look for a charge and those trusty jumper cables, read this quick guide on the door ajar sensor.

We will discuss how long the door ajar sensor takes to drain the battery, what causes a faulty door ajar switch, and how to prevent the battery from running out.

What Does A Door Ajar Switch Do?

will door ajar light drain battery

Door sensors are powered chiefly by your car’s electrical system. Every sensor installed in automobiles has a built-in function that shows whether or not an electronic current is open.

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A door ajar sensor indicates that the car’s door is left open, even when you think it’s properly closed.

Therefore, if a door isn’t fully closed, a dash icon will illuminate to remind you. Once the door is closed, the indicator light will go out.

Can A Door Ajar Switch Light Drain The Battery?

Yes, it can. A door ajar warning light can drain the car’s battery. Your car’s battery could die if you keep the door open for too long or when the caution light sensor stops working.

If you don’t completely shut the car’s doors, the internal illumination will keep sucking power out of the batteries.

I frequently get asked how I leave my doors open without draining my battery because when you open the doors, the interior lights go on! This is the case with most vehicles. Every automobile is different, but all newer vehicles should have some sort of control to turn interior lights on and off.

In some vehicles, you can activate the inside lights by keeping a door open even a little and if you leave your lights on long enough, your car’s battery will be drained. Luckily, this can be easily fixed with a jump-start, and in most cases, your battery will be just fine afterward.

How Long Does It Take For A Door Open Sensor To Drain The Battery?

The door opening sensor works through two mounts, creating an electrical current once they are parallel. One mount is on the door frame, while the other half is on the door.

Whenever the door shuts, a circuit is completed between the two components.

Once the door is open, the circuit gets broken since the magnet and switch are no longer close to one another.

The sensor sends signals to the control board whenever the link is broken. Even a dim headlight draws some power to maintain its illumination, which might quickly deplete your vehicle’s battery.

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A continuously illuminated door ajar sensor takes up to three hours to kill your car’s battery. So, when you see that your door ajar light is activated, shut every door completely.

Does the Sensor Drain Any Battery?

The door sensor can drain the battery even if the engine is off entirely. The door sensor consumes battery power even when the car is off since it continually checks the condition of the door.

As a consequence, the battery’s charge level will gradually fall. It’s important to remember, though, that this isn’t an everyday event, and most door sensors won’t affect the charge cycle much.

Other Potential Reasons For A Switched-On Door Ajar Warning Light

Your car’s door ajar warning light could also be on for various other reasons. Some of these causes are specific to its make and model. Let’s consider other causes for an illuminated door ajar light:

1. Dome light electrical fault:

The door ajar sensor may lighten up if the wire that connects the dome light to the vehicle’s electrical system gets damaged or short-circuits.

2. Anti-theft power circuit malfunction:

Anti-theft systems are installed in cars to protect them from thieves. The anti-theft system light alerts the user to illegal entry. An electrical malfunction in the anti-theft circuit can also affect the door ajar sensor, causing it to turn on.

3. A jammed door switch that won’t allow you to close it:

Latches on the doors can be problematic sometimes. The door ajar sensor will remain illuminated if the door latch doesn’t connect or close correctly. Additionally, jammed doors can also cause a door ajar sensor to malfunction.

4. Open wiring:

Exposed wires in your vehicle are an alarming issue that requires a prompt solution. When connected, these may lead to short-circuiting. One way or another, exposed wiring leads to switched-on warning lights.

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5. Electrical short circuit in doorway switch(es):

Short-circuiting seems to be the main culprit in causing the warning lights to turn on. Although this hardly ever happens, door switches can have electrical issues.

How To Diagnose and Fix A Malfunctioning Door Ajar Switch Sensor

A blinking external LED light indicates a misalignment in the door ajar sensors. If you spot this warning light, here’s how to fix it:

Licensed insurance agents recommend that a specialist should handle replacing your car’s door sensors as there are multiple possible causes for the issue. Yet, before you take your vehicle in for service, you must:

  • First, try opening and closing each door once more to be sure it’s not a fluke.
  • Then, apply WD-40 or another lube to each door’s frame and latch.
  • Give the lubricant a minute or two to penetrate the latch.
  • Lastly, ensure that all doors are closed securely.
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Effects Of A Defective Door Ajar Switch Light

A malfunctioning door ajar switch light can affect the performance of your car’s electronic control unit (ECU). The ECU is a crucial component that controls the car’s electrical functions and controls. A malfunctioning ECU can be dangerous in several ways:

  • Key fob control: The ECU handles connections with your key fob. A malfunction in the ECU can prevent your key fob from locking the doors.  
  • Door locking: An ECU malfunction can prevent you from locking the doors while the car is moving. Locking the doors while the car is moving is a significant safety concern, especially if children are on board.

Other Probable Reasons For Battery Drainage:

1. Lights left on:

The most frequent cause of a dead car battery is the driver forgetting to switch off the lights after.

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While some cars have headlights that switch off automatically after a while, even that small time frame can drain the battery significantly.

2. Parasitic drain:

Parasitic drain happens when parts of your car use energy from the 12-volt system after you’ve turned off the engine and taken the key out of the ignition. Powering features such as the timer, safety alarm, and auto locks rely on the battery bank.

If the electrical system is malfunctioning, however, more extensive components can continue working even while the car is off, draining the batteries.

3. Extreme weather:

Used or old car batteries will not live in extremely cold or hot situations as they are diluted. This is also true for most car batteries that have improved tolerance for high seasonal temperatures.

4. Alternator issues:

The battery won’t acquire a sufficient charge when the car’s alternator fails. Insufficient charging will drain the battery.

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How To Avoid Battery Depletion

Follow the steps below to keep your car’s battery healthy:

  • Before leaving the automobile, switch off all interior lights.
  • Clean your batteries. It’s crucial to do it often.
  • Make sure to examine battery cables and connections.
  • Use a portable battery charger or voltmeter to verify and recharge a low battery.
  • Lastly, take your automobile in for regular maintenance to prevent power loss.


What can drain a car’s battery even when it is switched off?

Several things might cause a car battery to discharge even when the engine is turned off. Leaving the interior lights on for an extended period can cause the battery to die. The door illumination being left on or faulty relays are two other potential causes.

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How do I turn off the door ajar indicator?

Try opening each door one at a time, and if you discover the light switch in the door frame, try pressing and releasing it for a few moments to see whether the light turns off.

Can the door ajar light drain my car’s battery?

Yes, a door ajar warning light can drain your car’s battery if left on for more than 3 hours. This can be due to a door being inadvertently open or even a malfunction in the door sensors.

Why is my door ajar warning light blinking even when all doors are closed?

The door ajar sensor works through the car’s ECU, which connects to the rest of the electrical systems. Several electrical systems in your car work even when it is off, like the dome light or anti-theft door sensors. A malfunction in either of these two systems can cause the door ajar light to switch on.

Meta description: Ever wondered whether your car’s battery died due to an ajar door? Well, wonder no longer for we have everything you’ll ever need to know about the door ajar warning light! Read now and find out!

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