Toyota C-HR Alarm Going Off? (16 Common Causes)

The Toyota C-HR is a unique subcompact SUV that was introduced in 2018.

Despite being a reliable model, alarm issues can occur.

If your C-HR’s alarm keeps going off, this article should help you resolve the issue.

Why Does My Toyota C-HR Alarm Keep Going Off?

A Toyota C-HR alarm is usually triggered by a faulty hood switch or door switch. Other common causes include a bad 12V battery, bugs in the cabin, not closing a door properly, key fob issues, and damaged wiring. 

1. Faulty Hood Switch

A faulty hood switch is a common cause of unwanted alarms for Toyota vehicles (C-HR 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 C-HR, 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 C-HR.

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.

  1. Inspect the battery and look for any signs of damage, dirt build-up, rust, or corrosion.
  2. Disconnect the battery and loosen the nuts on the clamps using a wrench.
  3. Remove the negative clamp, marked with a “-” first.
  4. 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.

“My CHR alarm keeps going off at night. Toyota had it in their repair shop yesterday. They said there was a corroded connector to the battery…” –

“Seemed to remember a similar problem being raised on this forum a few weeks ago, I think it was resolved by replacing the 12V battery…” –

4. Drained 12V Battery

A faulty or weakened car battery causes a variety of problems, including accidentally triggering the C-HR alarm.

The best thing to do is take your C-HR 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.

“In some cars an unexpected voltage drop can cause the alarm to sound (the alarm system interprets this as a door being opened/courtesy light coming on).” –

5. Interior Motion Sensors

Some Venza models have an interior motion sensor, which can be triggered by bugs inside the cabin.

If you can’t see any moths or bugs you can still try spraying the cabin with some bug spray.

You can also try disabling the interior sensors for a week or so to see if the problem is in fact linked to the interior sensors – there is a button on the roof to disable the sensors.

“This just happened to me last week. It was a moth inside the car. You can turn off the sensors as already said, by pressing the button on the roof.” –

6. Faulty Key Fob

Another reported cause of nuisance alarms on the C-HR 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.

Related: Toyota C-HR Keeps Beeping? (16 Common Causes)

7. Key Fob Running on Low Battery

A common cause of mysterious alarms on the C-HR 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.

8. 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 C-HR’s alarm. 

“Check that all the doors are shut and the bonnet[trunk]… –

9. Outdated Software

Vehicles that are as technologically sophisticated as this model are dependent on constant firmware and software updates. 

If you fail to update your vehicle’s software packages, you may encounter random errors and glitches, including the car’s alarm going off.

Always update your vehicle’s software modules to prevent any bugs, glitches, or errors. 

10. Water Leakage

Water leaking into the latches and sensors is quite common for owners of the C-HR. It is essentially a design flaw that can trigger the vehicle’s alarm.

While the quick fix is to wipe down vulnerable areas around your latches and switches, it would be much better to consult with auto mechanics to find a long-term solution (such as adding additional seals or rubber linings).

11. Rust and Corrosion on Door and Hood Latches

Rust and corrosion can also damage the latches and switches, which may trick the sensors into detecting that a door or the front hood is open.

If your car is frequently exposed to moisture or other external elements, then you should routinely inspect critical areas of your vehicle for any sign of rust or corrosion. 

12. 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. 

13. 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.

An expert on had this to say:

“There could be loose or damaged wiring connections affecting the alarm system. Visually inspect the wiring around the alarm system components, including sensors and control units, for any signs of damage or disconnection…”

14. Rodents Chewed Wiring

Due to the soy-based material used for certain cables and wiring, rodents would chew through certain components of the vehicle, alarm wiring included. To address this, make sure your vehicle is in a safe and enclosed area.

15. 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. 

16. Aftermarket Alarm Issues

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.

The aftermarket alarm may have overly sensitive sensors too.

“Might have a vibration detection type of alarm sensor. Been pretty windy recently, so maybe that has triggered it. A neighbor of mine has one of those alarms and it’s always going off when the wind picks up.” –

If you are experiencing issues with an aftermarket alarm, the best thing to do is speak with a reputable auto electrician. 

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: 5 Best & Worst Toyota C-HR Years (Pictures & Stats)



  • Ian Sawyer

    Growing up with a father who was a mechanic I had an appreciation for cars and motorcycles from an early age. I shared my first bike with my brother that had little more than a 40cc engine but it opened up a world of excitement for me, I was hooked. As I grew older I progressed onto bigger bikes and...