The Ford Mustang is one of the most iconic American muscle cars.
Despite being a finely tuned machine, it’s not uncommon for the alarm to go off at random.
If you’re Mustang alarm keeps going off, this article is here to help.
Why Does My Ford Mustang Alarm Keep Going Off?
The most common cause of the alarm going off on a Ford Mustang is due to a faulty hood latch sensor. Other causes include a dying 12V battery, interior sensor issues, a faulty body control module, a low key fob battery, a faulty door switch and a badly installed alarm system.
If your Mustang alarm is going off when it shouldn’t then by process of elimination, it shouldn’t be too tricky to find the root cause.
1. Hood Latch Sensor Problems
Like most cars the Mustang utilizes a hood latch sensor which is essentially an electrical switch.
It is designed to trigger an alarm if someone tries to force open the hood, however if it is broken or clogged with dirt this can trigger the alarm.
Dirty / Rusted Hood Latch Sensor
Due to the prominent location of the latch, it is very prone to getting dusty, dirty and grimy – the accumulation of which is enough to cause alarm issues. Corrosion and rusting of the hood switch is also very common, which can also trigger the alarm.
Here’s what one Ford owner had to say:
“I had this problem on mine year before last, hood open whilst driving and alarm randomly going off when locked. There is a micro switch inside the hood locking mechanism that had got stuck with gunk causing the problem, took it off and soaked in brake fluid overnight…not had a problem since.”
Brake fluid is made up of chemical compounds that evaporate as they dry, leaving no residue behind and dissolving grease for perfectly clean automotive parts.
It’s also a good idea to spray a little WD40 too for some much-needed lubrication.
Faulty Hood Latch Sensor
It’s not uncommon for the hood switch to develop a fault or get damaged from the bumps of driving, from slamming the hood. or exposure to weather
If the switch that monitors whether the hood is open or shut isn’t working then this can have a serious effect on the alarm.
You’ll need to look out for a plunger-like sensor that monitors whether the hood is open or not, and check to see if it’s in good working order.
Open the hood and look to the passenger side, the sensor is located right near the underhood fuse box – it looks like a black ribbed rubber part.
Here’s what a couple of Mustang owners had to say:
“For those of us that had it previously [alarm going off at random] it was the hood alarm triggering it. There is a “plunger” like sensor under the hood that goes bad.”
“Check the sensor under the hood – passenger side near the shock tower, looks like a plunger. That sensor sees the most weather and will go bad. Once it goes it trips the alarm because it reads the hood open. When you hit the lock button does your car sound the horn twice? That means it is reading a sensor as open. The sensor is only about $35 and easy to replace.“
2. Dying 12V Battery
A dying 12V battery or a battery with low voltage can cause a slew of problems, including activating the alarm of your Mustang. This should really be the first thing you check as it’s a very common cause and it’s easy enough to check and fix.
Most 12V car batteries last about 3-4 years so it might be time for a new one.
It’s always worth cleaning the terminals first though and making sure the connections are tight and free from dirt, gunk and debris.
Tip: Clean the terminals using a toothbrush dipped in baking soda and water mixture
Failing that, the next step is to check the battery, you can do this with a multimeter.
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.
If you’re not confident doing this, take your car to any AutoZone who often offers free battery health checks.
3. Water Leak Issues
If you drive a convertible Mustang then it’s always worth checking for any water leak issues especially around the Smart Junction Box and passenger footwell.
Needless to say, water and electronics don’t mix and this can cause a wide range of issues including alarm problems.
4. Faulty Body Control Module
A common reason why a Ford Mustang 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 Ford 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
5. Interior Motion Sensors
A common cause of the Mustang alarm going off is linked to the interior motion sensors.
The interior motion sensors are designed to detect movement inside your car, and they are located in the overhead console.
Sometimes insects and bugs might get trapped in the car or even leaves being blown in, which can be picked up by these sensors thereby triggering the alarm.
Some owners have complained that after leaving their dog in their car they’ve come back to find the alarm going off.
Give it a week of not arming the interior sensors by selecting the ‘Perimeter’ option instead of the ‘All Sensors’ setting which is the standard setting to see if this makes any difference.
- If you do not choose a setting when you exit the vehicle, the system defaults to all sensors.
- In perimeter sensing, the interior sensors are off when you arm the alarm.
Alternatively, you could cover the sensors over with something like electrical tape, although Ford does not advise this.
6. RFI and EMR
RFI is Radio Frequency Interference and EMR is electromagnetic radiation, both of which can cause the alarm to be triggered on your Mustang.
For example, parking underneath overhead power lines will expose your car to high amounts of EMR which can interfere with the electronics on your alarm system.
If you suspect this is the cause, try parking somewhere else out the way.
Here’s what one Ford owner had to say:
“There probably is some sort of RFI being generated around where you park at work which is making your car go insane.”
7. Faulty Door Lock Sensors
A faulty door latch sensor is a common cause of Ford Mustang alarms going off.
Similar to the hood latch sensor, your Mustang 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.
8. Low Key Fob Battery / Faulty Key Fob
As the key fob also has controls linked with your Mustang alarm system, a faulty, damaged or malfunctioning key fob can send an incorrect signal, which may trigger the alarm. A low key fob battery can cause the alarm on your car 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 also 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 also.
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.
In summary, if you suspect your problems might be key fob related you can try the following:
- Check and replace key fob batteries
- Clean the key fob
- Reset the key fob
- Reprogram the key fob
Here’s one owner’s advice:
“I’d say the first thing to try would be to spend the $6 and get a couple of new batteries for the FOB and if it still does it then you have a bigger problem. I always try to weed out the simple problems 1st. If $6 fixes the problem then you won’t have to spend any money taking the car to the dealer to diagnose the problem.”
9. Badly Installed Alarm System
Newer Mustangs come standard with an anti-theft system in place, with active anti-theft packages available too.
However, older Mustangs do not have anti-theft systems, so an aftermarket alarm system may have been installed.
Aftermarket alarm systems are notoriously installed improperly by the inexperienced. This can create all sorts of issues.
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 Ford Dealership
If needed, take your Ford 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 Ford 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 Ford’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.