The Toyota Mirai is one of the few fuel-cell electric vehicles available in the North American market today.
Like any car, its not immune from alarm issues.
If your Mirai’s alarm keeps going off, this article is here to help.
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Why Does My Toyota Mirai Alarm Keep Going Off?
A Toyota Mirai alarm is usually triggered by a faulty hood switch or door switch as these sensors are prone to defects or damage (over time). Other common causes include battery problems, key fob issues, and an incorrectly installed aftermarket alarm system.
1. Faulty Hood Switch
A faulty hood switch is a common cause of unwanted alarms for Toyota vehicles (Mirai included).
The switch is typically embedded in the hood latch.
The small electronic device is designed to detect whether the hood is open or shut and is an important part of the car’s alarm system – if it is broken, loose or dirty it can send false readings to the car’s computer thus triggering the alarm.
- Pop the hood and locate the hood switch.
- Check for any obvious damage, rust or loose connections.
- Give the hood switch a clean too (use contact cleaner), as dirt and grime can cause issues.
- You can test the switch with a continuity tester.
If you are well-versed mechanically, you can buy a new hood switch online and replace it yourself. Otherwise, we’d advise visiting your local mechanic.
2. Malfunctioning Door Switches
Faulty door switches (including the rear hatch) are another common cause of random alarms on the Mirai, similar to the hood switch, these switches monitor the open/closed status of the door – if damaged, faulty or dirty they can send false readings thereby triggering the alarm.
Door switches are a common point of failure as they are subject to wear and tear due to the doors being continually opened/closed/slammed etc.
The door latches and door switches can get dirty too which can cause issues, so the first thing you should do is give all door latches a good clean and spray some WD-40 on the latch and work it in to see if that helps.
Also check the wiring leading from the body into the door for any signs of damage, it should be in a flexible hose on the hinge side of the door.
If you suspect the alarm issues are linked to the door switch, ask your dealer to run a diagnostic test to try and pinpoint the fault.
3. Loose or Bad 12V Battery Connections
Loose or bad 12V battery connections can cause a number of problems, including triggering the alarm of your Mirai.
A bad connection can be caused by dirt or gunk buildup.
The terminals may have come loose from driving and vibrations etc.
Make sure the engine is off before doing any work on the battery.
- Inspect the battery and look for any signs of damage, dirt build-up, rust, or corrosion.
- Disconnect the battery and loosen the nuts on the clamps using a wrench.
- Remove the negative clamp, marked with a “-” first.
- Clean the terminals with a toothbrush dipped in a mix of baking soda and water, rinse with distilled water and dry with a cloth.
- Reconnect the battery, ensuring tight connections.
Related: Toyota Mirai Beeping? (13 Common Causes)
4. Drained 12V Battery
A faulty or weakened car battery causes a variety of problems, including accidentally triggering the Mirai alarm.
The best thing to do is take your Mirai for a battery health check, these are usually quite inexpensive or sometimes free such as at AutoZone.
Or you can test it yourself with a multimeter (see the guide at the end of this article).
A healthy 12V battery should be about 12.6 to 12.8 volts while a weakened battery reads below 12 volts.
5. Faulty Key Fob
Another reported cause of nuisance alarms on the Mirai is a faulty key fob.
If you have 2 remotes, try taking the battery out of one and use the other for a while.
If the alarm problems persist, and you have tried cleaning the inside of the fob(s) and changing the battery, the best thing to do is speak with your dealer.
6. Key Fob Running on Low Battery
A common cause of mysterious alarms on the Mirai is a low key fob battery. Similarly, if the fob is dirty or dusty this can also cause alarm issues.
Give the inside of your fob a clean and replace the battery to eliminate this possible cause. It’s worth spending a bit extra for a good brand of battery.
- To open your key fob, stick your prying tool into the slit or gap between the two halves of the outer casing and gently apply upward pressure to pop open the device.
- Remove the battery.
- Give the key fob a good clean to remove any dirt or fluff – a cotton swab and some rubbing alcohol should do the trick.
- Check for damage, rust or loose connection (you may need a new key fob depending on what you find).
- Be sure to insert the new battery facing the right way up.
- Assemble the outer casing of your key fob by clamping them back together.
“Battery in my key fob has died on my, used my key to open my car and CAR ALARM ATTACK…” – ToyotaOwnersClub.com
7. Not Closing Doors, Hood, or Trunk Properly
Something as simple as not properly closing the doors, hood, or trunk will inevitably trigger the alarm.
Make sure to check if you have closed every point of entry of your vehicle to avoid accidentally tripping your Mirai’s alarm.
8. Faulty Body Control Module (BCM)
A faulty body control module can cause a wide range of issues including nuisance alarms.
- The BCM is in charge of electrical communication from different electronic systems.
- This includes the car alarm system, lock-unlock functions, climate control etc.
If you feel that your BCM is the culprit behind random alarm activation, then book an appointment with your local dealership to have it inspected.
9. Damaged Wiring
Damaged electrical wiring can cause a wide range of problems, it can often be tricky to pinpoint too and you may need to have an auto electrician run some diagnostic tests.
The wiring may have been chewed by rodents, you can inspect the car for clues and see if you can spot any chewed wires, or speak to your dealership to run some diagnostic tests.
10. Animals Climbing On The Vehicle
If your alarm has been set off in the middle of the night, it may have been by an animal climbing on the car.
States such as Illinois, Indiana, Iowa, Texas, Wisconsin, and Carolina have large wild raccoon populations.
Have a look for footprints on the hood and the roof.
If you have a CCTV system, examine the footage. These animals usually appear during the night.
11. Incorrectly Installed Aftermarket Alarm
An incorrectly installed or faulty aftermarket alarm system is a common cause of nuisance alarms.
Aftermarket alarms are typically far more complex than any factory-installed equipment which makes them more prone to issues.
They may also have been installed by incompetent individuals.
If you are experiencing issues with an aftermarket alarm, the best thing to do is speak with a reputable auto electrician.
“Is it aftermarket? I know someone who has an issue because of the alarm being installed later.” – Reddit.com/r/Toyota
Alternative Suggestions
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.
Disconnect the Battery
Sometimes mysterious alarm problems can disappear with a simple reboot, there are no guarantees here but it’s worth a try.
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 instrument panel?
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 your unit is still under warranty then they should fix and resolve the issue for free.
How to Test the 12V Battery
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: 8 Best & Worst Toyota Mirai Years (Facts & Stats)
Sources
https://www.toyota.com/owners/resources/warranty-owners-manuals
