Known for its striking design, the Sonata is a top pick in the mid-size sedan segment.
As with any car, nuisance or random triggering of the alarm isn’t uncommon.
If your Sonata car alarm keeps going off, this article is here to help…
Table of Contents
Why Does My Hyundai Sonata Alarm Keep Going Off?
The main causes of the Hyundai Sonata alarm going off at random are hood switch pad issues, a faulty hood switch, faulty sensors, low key fob battery, a weak or dying 12V battery, accidental press of the panic alarm, wiring issues, aftermarket alarm issues, and electrical interference.
1. Faulty Hood Switch Pad
A very common reason why the Hyundai Sonata alarm keeps going off is due to issues with the hood switch pad (the rubber stopper that depresses the hood switch) usually it has gone missing, isn’t thick enough or has collapsed slightly.
The hood switch is designed to detect the forcing open of the hood, issues with the switch pad have been attributed to numerous false alarms for owners.
This issue is so widespread that Hyundai issued a technical service bulletin (TSB 09-BE-026. The bulletin applies to other Hyundai vehicles as well.
Hyundai attributes the problem to light contact with the hood switch pad and the hood switch. Hyundai has revised the part. The new part #92736-3A000 is available from the dealer. To install it, open the hood and remove the rubber switch pad located on the front driver’s corner of the hood. Install the new switch pad. After the pad is installed, press the LOCK button on the transmitter. The doors should lock and the hazard lights should flash once. Then press the LOCK button twice and you should hear the horn. That tells you the system is operational.
2. Faulty Hood Switch
A very common reason why the Sonata alarm may be triggered at random is due to issues with the hood switch (not to be confused with the rubber switch pad).
The first thing you should do is locate the hood switch and make sure that it is free of any dirt, grime or gunk.
It’s also possible to test across the hood switch with a continuity tester, if you’re technically inclined, to see if it’s working as it should.
If you have inspected the hood switch and you suspect it’s faulty, have a mechanic or your local Hyundai dealer take a look.
On Hyundai-Forums.com, here’s what Sonata owners had to say:
“It’s more than likely the hood switch as it’s a common Hyundai problem and much easier to fix that than disabling the alarm.”
“The problem turned out to be the switch under the hood that was connected to the alarm.”
3. Faulty Sensors
Aside from the hood switch, there are door sensors (switches) and a trunk switch that could be faulty. These simple mechanical devices, when damaged, dirty or broken can cause random alarms as they are an integral part of the alarm system.
The switches simply detect if the door, trunk or hood is closed when the alarm is armed. They can give false readings when faulty.
If you suspect you have a faulty switch you can take your car to your nearest dealer and have them perform some scans/tests.
On HyundaiForum.com, here is what Sonata owners had to say:
“Maybe one of your door sensors is going bad and causing random alarm issues?”
“One of the door/hood/trunk sensors are bad or misaligned. Check the hood first as that’s usually the problem. Make sure the hood and all doors are closed all the way.”
4. Low Key Fob Battery or Faulty Key Fob
A low key fob battery is a common cause of mysterious alarms on the Sonata, and many car models for that matter. To rule out this potential cause, it’s a good idea to replace the batteries in your key fobs.
- Most Sonatas use a CR2032 battery (double check first though), make sure you insert it the right way up, and it’s best to buy a reputable brand of battery.
- Check that the inside of the fob is clean too, you can clean dirt and debris with a cotton swab and some rubbing alcohol.
Some Hyundai models are known to trigger the panic alarm as a way to signal that the battery in the fob is running low.
Here is a useful suggestion from one Sonata owner on Hyundai-Forums.com
“Take the battery out of the remote(s) and don’t use them for a few days. This will eliminate the remote from the equation. If it still occurs then you know its not the remotes.”
Similarly, a faulty key fob can also trigger random alarms. Although this is much less common.
If you suspect your fob might be faulty, speak with your local Hyundai dealer.
5. Dying or Weak 12V Battery
A Sonata‘s alarm can be triggered at random due to a weak or dying 12V battery. When the battery’s voltage is insufficient, it can cause the alarm to go off unexpectedly.
- Typically 12V car batteries have a lifespan of about 3 to 5 years and so it might be time for a replacement.
- Before swapping your car’s 12V battery, it is worth taking the time to disconnect the battery, clean the battery’s terminals, reconnect the battery, and ensure that the connections are tight and there are no obstructions.
- You can clean the terminals using a toothbrush dipped in baking soda and water mixture.
If you have a multimeter in your garage, you can do a battery check yourself – we’ve included a short guide at the end of this article – essentially the battery should measure between 12.2 and 12.6 volts.
If you’re unsure, take your car to your nearest AutoZone – most offer free battery health checks.
6. Accidental Press of the Panic Alarm
One simple and often overlooked reason for a false alarm on the Accent is accidentally pressing the panic alarm on the key fob.
This can be easily done when the fob is in your pocket, especially when wearing tight clothes or bending down to pick something up.
Here is what the Sonata’s owner’s manual says:
“Press and hold the Panic button for more than one second. The horn sounds and hazard warning lights flash for about 30 seconds. To cancel the panic mode, press any button on the remote key.”
7. Aftermarket Alarm System
If your Sonata has an aftermarket alarm fitted (one that did not come fitted as standard with the car) then this may have been incorrectly installed or it may be faulty.
It may also have additional sensors which might be damaged or overly sensitive.
Aftermarket alarm systems are often more sophisticated than a typical 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 your nearest Hyundai dealership or an auto electrician.
8. Electrical Wiring Damaged
Damaged electrical wiring can cause a wide variety of issues, especially with the alarm system.
Damaged, corroded or faulty wires aren’t easy to find and you’ll need to have an auto electrician carry out some fault finding on your car.
A common point of failure for electrical wiring is in and around the doors,.
If you’ve had some kind of water leak in your car then this issue is one to investigate.
9. Electrical Interference
Parking underneath or within close proximity of overhead power lines can cause false alarms from your Sonata.
If you notice your alarm goes off, but only in certain locations, then it could be some kind of electrical interference from power lines or even a HAM radio.
This phenomenon is caused by electromagnetic radiation (EMR) which can interfere with the electronics of your alarm system.
If you suspect this is the cause, try parking somewhere else out of the way.
If you have the Bluelink app you can check this for clues as to why your alarm is going off.
It is best to check the app when the alarm is going off.
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.
Make Sure All Doors Are Shut Properly
This is sometimes overlooked, but make sure all doors, trunk and hood are shut properly.
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 Open’.
Take it to a Hyundai Dealership
If needed, take your Sonata 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 car 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 Hyundai’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.
One TSB that is alarm related, for the Hyundai Sonata is TSB 09-BE-026.
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.
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.