The Ford Focus was officially put to rest in 2018 after two decades of production, as the SUV models take priority.
Despite being a well-built compact car, it’s not uncommon for the alarm to go off at random.
If you’re Focus alarm keeps going off this article is here to help.
Why Does My Ford Focus Alarm Keep Going Off?
The most common cause of the alarm going off on a Ford Focus is due to a low 12V battery. Other causes include high shock sensitivity, a faulty body control module, a low key fob battery, a faulty hood switch and electromagnetic interference.
If your Focus 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. 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 Focus. 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.
2. Faulty Body Control Module
One of the most common reasons why a Ford Focus alarm keeps going off is due to a faulty body control module.
If your Focus alarm goes off in the middle of the night 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
You may also like: 7 Most Common Ford Focus Problems (Explained)
3. Hood Latch Sensor Problems
Like most modern cars the Focus features 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 Focus 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 Focus to your local mechanic to take a look.
Here’s one owner’s tip:
“Look for the electrical connector directly attached to the hood latch and make sure it’s still connected and the wires are not frayed or damaged. That would be the most obvious place to start.”
4. 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 Focus.
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 Focus 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.”
5. Faulty Door Lock Sensors
A faulty door latch sensor is a common cause of Ford Focus alarms going off.
Similar to the hood latch sensor, your Focus 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.
6. Low Key Fob Battery / Faulty Key Fob
As the key fob also has controls linked with your Focus 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. Aftermarket Alarm Systems
Aftermarket alarms are not made by the original equipment manufacturer, these are generally more susceptible to faults and problems, especially when they’ve been installed by a novice or installed incorrectly.
If you have an aftermarket alarm that’s faulty and causing you problems then you might need to have it disabled, removed or replaced.
If you’ve recently had a new alarm system installed 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 Focus 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 as when a cat touches your car or in 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 one owner describes adjusting the sensitivity of a Ford Focus’ shock sensors:
- The first step is to 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.
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.