The Ford Fiesta was discontinued in the USA in 2019 after a production run that lasted just over four decades.
Despite being a solid subcompact car, it’s not uncommon for the alarm to go off for seemingly mysterious reasons.
If you’re Fiesta alarm keeps going off this article is here to help.
Why Does My Ford Fiesta Alarm Keep Going Off?
The most common cause of the alarm going off on a Ford Fiesta is due to a faulty hood latch sensor or failed door latch. Other causes include a dying 12V battery, high shock sensitivity, a faulty body control module, a low key fob battery and a corroded plug for the alarm harness.
If your Fiesta alarm is going off when it shouldn’t then by process of elimination, it shouldn’t be too tricky to narrow down the root cause.
1. Hood Latch Sensor Issues
Like most cars the Fiesta utilizes a hood latch sensor which is a simple electrical switch.
It is designed to trigger an alarm if someone tries to force open the hood – if it is broken or dirty it can trigger the alarm.
Dirty / Rusted Hood Latch Sensor
Over time due to the location of the latch, it is very prone to getting dusty, dirty, grimy and covered in gunk – this alone is enough to cause the alarm to go off at random. 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 or from slamming shut the hood.
If the switch that monitors whether the hood is open or shut isn’t working then this can trigger the alarm.
It’s not overly technical to test, you’ll need a multimeter / continuity tester and you can test across the switch to see whether it is correctly opening and closing the electrical circuit.
The beeping sound from the tester indicates a closed circuit, the beeping will stop when there is an open circuit.
If you’re unsure, take your Fiesta to your local mechanic to take a look.
Here’s one Fiesta owner’s success story:
“It was my hood latch. The latch has a sensor that i closed the loop on with a paper clip. Then before I had to get my state inspection done, i replaced it with a new door latch from Ford.”
2. Faulty Door Lock Sensors
A faulty door latch sensor is a common cause of Ford Fiesta alarms going off.
Similar to the hood latch sensor, your Fiesta 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.
Important: The Ford Fiesta was well known for having door latches that were prone to failure, thus causing alarm problems.
The problem stems from the latch pawl’s spring-tab design, which was known to degrade in hot weather conditions.
Ford recalled just shy of 250,000 vehicles for this issue and despite lots of Fiesta models being affected, only certain 2014-2015 models were recalled.
3. Dying 12V Battery
A dying 12V battery or a battery with insufficient voltage can cause a wide range of problems, including triggering the alarm of your Fiesta. This should really be the first thing you check as it’s a very common cause and it’s easy enough to fix.
Most 12V car batteries last about 3-4 years so it might be time for a new one.
It’s worth cleaning the terminals first though and making sure the connections are tight and free from dirt and debris.
Tip: 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.
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.
4. Faulty Body Control Module
A common reason why a Ford Fiesta alarm keeps going off is due to a faulty body control module.
If your Fiesta alarm goes off in the middle of the night or at random hours then this is certainly something you should have looked at.
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 $500 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. 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 Fiesta.
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, simply park 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.”
6. Low Key Fob Battery / Faulty Key Fob
As the key fob also has controls linked with your Fiesta 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 owners 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.”
7. Badly Installed Alarm System
If you’ve recently had a new alarm system installed on your Fiesta you might need to go and speak to the mechanic who fitted it and explain your problem.
If you installed the alarm system yourself then you may have made a mistake and will need to double-check everything using the installation manual.
8. Overly Sensitive Sensors
On Ford Fiesta models there is often a shock sensor connected to the factory alarm – if the sensitivity is turned all the way up, then the alarm will go off very easily such windy conditions.
Shock sensors detect hits and impacts around your car e.g. if someone smashes a window the sensor detects this and sends a signal to the alarm’s computer.
Here’s how to adjust the Ford Fiestas shock sensors:
- Locate the alarm.
- Typically it is a black box – usually an inch thick by 3 or 4 inches by 5 or 6 inches.
- Ford usually uses CODE or KARR alarms.
- Try pulling down the plastic driver side under the dash panel, and then the metal plate under that (held in with bolts).
- You should see the alarm brain now.
- It should be able to be pulled out from the dash (maybe zip tied or even just tucked up there).
- Don’t unhook the wires though.
- On this box should be a little twisty screw (flat blade).
- Typically right turning is more sensitivity, left turning is less.
- This is a shock sensor.
- Typically, at least when an alarm is properly installed, you want the shock sensor to be zip tied to a solid metal part of the car.
- That way, vibrations through the car will go to the box.
If you can’t find the control knob then you may have a system that will need to be programmed in order to adjust sensitivity, in which case you’ll have to get the dealer to turn down the sensitivity.
9. Corroded Plug For the Alarm Harness
Although this one is a bit ambiguous we thought it was worth mentioning…
On the popular fiesatstforum.com one owner described how their alarm would go off at random in the night, this was another owners response:
“A guy I know with his Fiesta had a similar issue. It was a corroded plug for the alarm wire harness. Can’t remember where but if you can find the alarm wiring schematic you may want to check everything that it is tied to it.”
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:
There has been a door latch recall for certain 2014 and 2015 Fiestas – problems with door latches go hand in hand with alarm problems.
According to cars.com, here are the details:
A component within the door latches may break making the doors difficult to latch and/or leading the driver or a passenger to believe a door is securely closed when, in fact, it is not.
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.