The 4Runner is a great midsize SUV that is capable of serious off-roading trips.
Like any other vehicle, it’s not unusual for problems to occur with the alarm system.
If your Toyota 4Runner alarm keeps going off this article is here to help.
Why Does My Toyota 4Runner Alarm Keep Going Off?
A Toyota 4Runner alarm can be set off due to a faulty hood switch. Other common causes include a dying 12V battery, a faulty key fob, faulty door sensors, a low key fob battery, overly sensitive sensors, wiring problems or a faulty body control module.
If your 4Runner alarm is going off when it shouldn’t then by process of elimination, it shouldn’t be too hard to narrow down the root cause.
1. Faulty Hood Switch
A common cause of the alarm going off on the Toyota 4Runner is a faulty hood switch.
Due to their location, hood switches often get dirty and clogged up so it’s worth giving it a clean and some lubrication first.
The hood switch (sensor) is a simple electrical switch, that monitors whether the hood is open or closed.
You may even notice a hood ajar message pop up when you’re driving.
If the sensor completely fails you may see a hood ajar message constantly on.
If you suspect the hood switch is faulty and your car is still under warranty we recommend taking it to the dealer and having them replace it for free.
If you’re mechanically inclined you can simply replace the hood switch yourself, these can be picked up for under $100.
2. Faulty Key Fob
A faulty key fob can cause problems with the alarm system. Try using a replacement key fob to see if the alarm problems stop.
You can also ask your local dealer to repair your key fob as a new one can be very expensive.
3. Low Key Fob Battery
If your 4Runner has a low key fob battery this can trigger the alarm to go off at random.
Try using your spare coded key – if the problem goes away then you know you’ll need to replace the battery in your primary key fob.
It’s advised that you don’t carry big metal objects, electronics or a second coded key on the same keyring as your primary key fob as this can lead to problems starting your 4Runner.
It might also be worth giving the inside of your key fob a clean as these can get filled with dirt which could be causing the alarm issue.
4. Dying 12V Battery
A dying 12V battery or a battery with insufficient voltage can cause a wide range of problems, including triggering the alarm.
Most 12V car batteries last about 3-4 years so it might be time for a replacement.
It’s worth cleaning the terminals first though and making sure the connections are tight and free from dirt and debris.
Clean the terminals using a toothbrush dipped in baking soda and water mixture.
The next step is to check the battery, you can do this with a multimeter or take your car to any AutoZone who often offers free battery health checks.
How to Test the Battery
- Before testing, remove the surface charge from the battery, this allows for an accurate reading.
- Simply turn on the headlights for 2 minutes then turn off.
- Set the multimeter dial to the ’20 Volts’ setting.
- Make sure the car is turned OFF
The multimeter will have a red probe and a black probe:
- The red probe is for making contact with the positive terminal
- The black probe is for making contact with the negative terminal.
Measure across the battery terminals.
- The meter should display a reading, if the battery is fully charged the voltage should be between 12.2 and 12.6 volts.
- Anything under 12V and the battery should be charged or replaced.
Related: 21 Best & Worst Toyota 4Runner Years (With Facts & Stats)
5. Overly Sensitive Alarm Sensors
You can ask your dealership or local mechanic if the alarm sensitivity can be adjusted.
Many alarm systems have movement sensors that are meant to trigger if an attempt is made to tow the car.
If these are too sensitive, they can be set off by a strong gust of wind or even by a cat jumping on the car.
There can also be Glass Breakage Sensors (GBS) that are meant to trigger on the sound of a window being broken that can also be overly sensitive.
6. Corroded or Rusty Battery Terminals
If your 4Runner has rusted battery terminals it will be unable to deliver the correct electrical power to various parts of the car.
The alarm system will often interpret this as a low-battery scenario and trigger the alarm.
Rusting can be caused by moisture and road salt exposure but also by improper charging.
- When a battery is undercharged it is common to see corrosion form on the negative terminal.
- Similarly, an overcharged battery will see corrosion form on the positive terminal.
Corroded battery terminals and posts can be cleaned by applying baking soda and scrubbing with a wet toothbrush.
If the battery terminals are severely rusted you will need to replace the battery.
7. High Voltage Power Lines
Parking underneath overhead power lines can trigger the alarm on your Toyota 4Runner.
This phenomenon is caused by electromagnetic radiation (EMR) which can interfere with the electronics on your alarm system.
If you suspect this is the cause, simply park somewhere else out the way.
Depending on where you live this may not be relevant as power lines can often be located underground.
Related: Toyota 4Runner Beeping? (11 Common Causes)
8. Faulty Interior Motion Sensor
Sometimes faults develop with the interior motion sensors, this can cause the alarm to be triggered at random.
Although this is less of a common occurrence it can and does happen.
9. Faulty Door Lock Sensors
A faulty door latch sensor is a common cause of 4Runner alarms going off.
Similar to the hood latch sensor, your 4Runner alarm monitors the doors to make sure no one is opening them.
It’s a good idea to give all door latches a clean and some lubrication with WD-40.
If you suspect the door lock sensor is faulty and your car is still under warranty we recommend taking it to the dealer and having them replace it for free.
10. Faulty Body Control Module
A common reason why a 4Runner alarm keeps going off is due to a faulty body control module.
The body control module or ‘body computer’ is the electronic control unit responsible for monitoring and controlling various systems associated with the vehicle’s body such as the alarm, immobilizers, power windows etc.
The body control module can develop corrosion on the pins or connections can become loose.
You can typically pick one up for around $650 and if you’re not mechanically inclined it’s probably best to have someone at Toyota fit it for you.
Other common symptoms of a bad BCM include:
- Repeated battery drain
- Starting problems
- Erratic electrical functions e.g. horn, wipers, lights, lights on the dash
- Security and alarm system problems
11. Damaged Wiring
Damaged electrical wiring can cause a wide range of problems.
Wiring damage can occur from general wear and tear or even from rodents chewing on the wiring.
Broken wires aren’t easy to find and you’ll need to have an auto electrician carry out some basic tests on your vehicle.
A common point of failure for electrical wiring is in and around the doors.
12. Incorrect Installation of a New Alarm
If you have recently had a new alarm fitted and it’s going off at random, then there’s a good chance it was installed incorrectly.
Your best option is to go back to the mechanic who installed it and explain your problem.
13. Aftermarket Alarms
If the car has an aftermarket alarm fitted (one that did not come as standard with the vehicle) then this may have been incorrectly installed.
It may also have overly sensitive sensors which can be triggered by strong wind or even a cat or dog.
These alarm systems are often more sophisticated than a basic factory-installed car alarm but are often installed by people who aren’t mechanics.
If you have an aftermarket alarm that’s causing you problems it’s best to have it examined by a trained auto electrician.
Disconnect the Battery
Sometimes mysterious alarm problems can disappear with a simple reboot, there are no guarantees here but it’s worth a shot.
Disconnect the battery for 20 seconds and this resets many of the electronics in the vehicle.
Check For Warning Messages
When the alarm occurs can you see any lights or warning messages on the gauge cluster?
This can give a clue as to what’s causing the alarm e.g. ‘Hood Ajar’.
Take it to a Toyota Dealership
If needed, take your Toyota to the dealership.
Tell them you are NOT paying for a check on what the problem might be.
Ask them if they will check it for free.
Most dealerships and other places do quick/initial diagnosis for no money as they plan to make money for the repair of your vehicle.
If you’re Toyota is still under warranty then they should fix and resolve the issue for free.
Check for Recalls or TSBs:
By entering your car’s VIN number on Toyota’s recall page or the NTHSA’s Safety Issues & Recalls page you can determine whether or not there is a TSB or recall for your vehicle and if there is you’ll want to get it addressed.
A recall is issued by a vehicle manufacturer for issues that are safety-related, while a TSB covers components that may be malfunctioning but don’t compromise the safety of the vehicle.
Related: Toyota 4Runner: 12 Common Problems (Solution Guide)