The Ranger is one of America’s best-selling mid-size pickup trucks.
Like any other vehicle, it’s not unusual for owners to have problems with the alarm system.
If you’re Ford Ranger alarm keeps going off this article is here to help.
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Why Does My Ford Ranger Alarm Keep Going Off?
The most common cause of the alarm going off at random on a Ford Ranger is due to the interior motion sensors being triggered by a moth or flying insect. Other causes include high shock sensitivity, low key fob battery, faulty hood switch and a low 12V battery.
If your Ranger 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. Interior Motion Sensors
The most common cause of the Ranger alarm going off is the triggering of the interior motion sensors.
The idea behind these is that it lets you keep your window open – but the alarm will go off if someone reaches in your truck to steal something like you’re phone or iPad – the sensors are aimed at and are monitoring the four windows.
The sensors are located in the roof console, two on the left and two on the right, in a square formation – they are round/circular looking and run in line with the roof console lights.
Sometimes insects and bugs might get trapped in the truck or even leaves being blown in, which can be picked up by these sensors thereby triggering the alarm – this is extremely common.
Some owners have complained that after leaving their dog in the truck 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, push ‘Ok’ to set. You will have to do this each time you turn off / exit the truck, and see if this stops the alarm from going off.
Note: If nothing is selected the truck will default to both interior and exterior sensors every time. It is not possible to default to ‘Perimeter’.
In Advanced Settings/Vehicle, you can select 1 of 3 choices:
- All Sensors (turns on the interior sensors)
- Prompt every time
If you’re often leaving dogs inside, ‘Prompt Every Time’ which is the same as ‘ask on exit’ is probably the best option.
As soon as you turn the truck off, you can use the up/down arrows on the steering wheel to select the appropriate mode for that cycle.
Alternatively, you could cover the sensors over with something like electrical tape.
Don’t take out word for it, here’s what the owners over at ford-trucks.com have to say:
“More than likely there’s a bug flying or crawling around inside of your vehicle when the alarm is set and the interior motion sensors are picking up the movement of said bug and that’s what’s triggering the alarm.“
“Did a quick forum search on the problem and this thread with the “bug tip” and headed to the truck, opened the door and a large moth-like bug immediately flew out. Problem solved.”
“Yep, probably a bug. You can try setting it to perimeter only.”
2. Dying 12V Battery
A dying 12V battery or a battery with insufficient voltage can cause a wide range of problems, including triggering the alarm.
Most 12V car batteries last about 3-4 years so it might be time for a replacement, 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 truck 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 truck to any AutoZone who often offers free battery health checks.
3. Shock Sensor Sensitivty
On the Ranger 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.
Shock sensors detect hits and impacts around your truck, e.g. if someone breaks a window the sensor detects this and sends a signal to the alarm’s computer.
- The sensitivity setting for this alarm should be mounted to the driver’s side vent tube.
- Open the door and remove the access panel on the side of the dash.
- There will be a black box mounted with zip ties.
- There should be a little black knob with white markings in a half-moon shape around – this controls the sensitivity. It looks a bit like a volume control knob.
Failing that look under the dash – the backside of the OBD-II port should have another connector that it’s plugged into, probably zip-tied to it.
If so, follow it up to the Vehicle Speed Sensor (black box), it shouldn’t be more than a foot away.
If you can’t find the control knob then you may have a system that will need to be programmed in order to adjust sensitivty, in which case you’ll have to get the dealer to turn down the sensitivity.
4. Faulty Hood Latch Sensor
A common cause of the alarm going off on the Ford Ranger is due to a faulty hood latch sensor otherwise known as a hood switch.
Due to their location, hood switches often get dirty and clogged up so it’s worth giving it a clean first.
The hood sensor is a simple electrical switch, that monitors whether the hood is open or closed (it’s a small rubber stump that’s black).
You may even notice a hood ajar message pop up when you’re driving.
If the sensor completely fails you may see the hood ajar message constantly on.
If you suspect the hood switch is faulty and your truck is still under warranty we recommend taking it to the dealer and having them replace it for free.
If you’re mechanically inclined you can simply replace the hood switch yourself, these can be picked up for $40 – $80.
One owner on Ford-Trucks.com had this to say:
“I unplugged the hood sensor at that seems to have fixed it. Just need the dealer to install a new one now.”
5. Low Transponder Key Battery
A low key fob battery can trigger the alarm on Rangers 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 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 starting your Ranger.
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.
6. Corroded or Rusty Battery Terminals
If your Ranger has rusted battery terminals it will be unable to deliver the correct electrical power to various parts of the car.
The alarm system will often interpret this as a low-battery scenario and trigger the alarm.
Rusting can be caused by moisture and road salt exposure but also by improper charging.
- When a battery is undercharged it is common to see corrosion form on the negative terminal.
- Similarly, an overcharged battery will see corrosion form on the positive terminal.
Corroded battery terminals and posts can be cleaned by applying baking soda and scrubbing with a wet toothbrush.
If the battery terminals are severely rusted you will need to replace the battery.
7. High Voltage Power Lines
Parking underneath overhead power lines can trigger the alarm on your Ford Ranger.
This phenomenon is caused by electromagnetic radiation (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.
Depending on where you live this may not be relevant as power lines can often be located underground.
8. Faulty Interior Motion Sensor
Sometimes faults develop with the interior motion sensors, this can cause the alarm to be triggered at random.
Although this is less of a common occurrence it can and does happen.
Here’s one owner’s story, from PowerStroke.org:
“Mine did that on one of my vehicles. Always in the middle of the night, too! I took it in and turned out, there was a faulty motion sensor that was causing my issue. They tried adjusting sensitivity several times, but once they replaced the sensor, I never had another problem with it.”
9. Faulty Door Lock Sensors
A faulty door latch sensor is a common cause of Ranger alarms going off.
Similar to the hood latch sensor, your Rangers 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 truck is still under warranty we recommend taking it to the dealer and having them replace it for free.
10. Faulty Body Control Module
A common reason why an Ranger 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
11. Damaged Wiring
Damaged electrical wiring can cause a wide range of problems.
Wiring damage can occur from general wear and tear or even from rodents chewing on the wiring.
Broken wires aren’t easy to find and you’ll need to have an auto electrician carry out some basic tests on your vehicle.
A common point of failure for electrical wiring is in and around the doors.
12. Incorrect Installation of a New Alarm
If you have recently had a new alarm fitted and it’s going off at random, then there’s a good chance it was installed incorrectly.
Your best option is to go back to the mechanic who installed it and explain your problem.
13. Aftermarket Alarms
If the car has an aftermarket alarm fitted (one that did not come as standard with the vehicle) then this may have been incorrectly installed.
It may also have overly sensitive sensors which can be triggered by strong wind or even a cat or dog.
These alarm systems are often more sophisticated than a basic 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 a trained auto electrician.
If you’re technically inclined then you can use FORScan to find out what has triggered the alarm.
Here’s one owner’s success story from the PowerStroke.org forum
“My alarm had been going off the last couple nights for no obvious reason. I used forscan to look up the last 2 alarm events. Both said hood ajar switch. Switch is in back of hood latch and looks like it was corroding inside. Bypassed for now as it fell apart during inspection. It doesn’t look like the type of switch that should be out in the elements.”
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.