The Trailblazer is a popular subcompact SUV that was previously a midsize SUV.
Like any vehicle, its not uncommon for the alarm to go off at random.
If your Trailblazer’s alarm system keeps sounding off, continue reading this article.
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Why Does My Chevrolet Trailblazer Alarm Keep Going Off?
A Chevrolet Trailblazer alarm is usually triggered by a weakened 12V battery, key fob issues, manually unlocking the vehicle with a key, a failing door or hood switch, aftermarket alarms, damaged wiring or a faulty BCM.
1. Drained or Faulty 12V Battery
A faulty or weakened car battery causes a lot of different problems, including accidentally triggering the Trailblazers alarm system. It is one of the most common causes of nuisance alarms.
The best thing to do is take your Trailblazer for a battery health check, these are usually quite inexpensive or sometimes free such as at AutoZone.
Or you can test it yourself with a multimeter (see guide at the end of this article).
A battery at full capacity should be about 12.6 to 12.8 volts while a weakened battery reads below 12 volts.
Prior to doing so, you should check that the battery terminal connections are tight and clean of gunk/dirt/grime/rust.
Make sure the engine is off before doing any work on the battery.
- Inspect the battery and look for any signs of damage, dirt build-up, rust, or corrosion.
- Disconnect the battery and loosen the nuts on the clamps using a wrench
- Remove the negative clamp, marked with a “-” first
- Clean the terminals with a toothbrush dipped in a mix of baking soda and water, rinse with distilled water and dry with a cloth.
- Re-connect the battery, ensuring tight connections
2. Key Fob Issues
The key fob is intricately linked to the Trailblazers alarm system, if it is dirty, damaged or low on battery, the alarm can be triggered at random.
The most common reason is usually a flat or weakened key fob battery.
For the sake of a few bucks it’s worth replacing the battery in your fob(s), and its also worth spending a bit extra for a good brand of battery.
Whilst you have the fob open to change the battery, give the inside a good clean.
Dirt buildup and dust can cause issues with the electronics.
- To open your key fob, stick your prying tool into the slit or gap between the two halves of the outer casing and gently apply upward pressure to pop open the device.
- Remove the battery.
- Give the key fob a good clean to remove any dirt or fluff – a cotton swap and some rubbing alcohol should do the trick.
- Check for damage, rust or loose connection (you may need a new key fob depending on what you find)
- Be sure to insert the new battery facing the right way up.
- Assemble the outer casing of your key fob by clamping them back together.
3. Manually Unlocking the Vehicle with Key
A number of Trailblazer owners have reported that manually unlocking their vehicle with the key (as opposed to using the key fob) has triggered the alarm. This is because the vehicle has been designed to be unlocked with the fob.
This is a common feature across many Chevrolet models.
Here’s one owners post from JustAnswer.com:
“05 chevy trailblazer. My alarm goes off if I dont unlock the car with the remote. The problem is that i think my remote just die and im at work.”
Here is a post from the forum gmtnation.com:
“Have an 06 Trailblazer LS that is driven by my son. It has what I’m sure is an aftermarket remote door unlock system… The thing has always acted sketchy off and on, but for the last month or two, the remotes don’t lock/unlock the doors at all. So now, when he parks the truck, son uses the button on the door to lock the truck, then uses his key to unlock. Problem is, 99.9% of the time, this triggers the alarm which is getting embarrassing. Almost thought about disconnecting the horn, but it was not a good idea.”
4. Door Switch Issues
A very common cause of a false alarm on a Chevy Trailblazer is a faulty door switch.
- The door switch is an electrical switch, located inside the latch.
- It monitors the state of the door, when the alarm is armed the door should be shut.
- If the switch is dirty, faulty or broken it can trigger false alarms.
It’s a good idea to give all latches a good clean and spray some WD40 to see if that remedies the situation.
Due to the doors being continually opened and closed, the door switch is prone to failure.
If you take your Trailblazer to the dealership they should be able to run some diagnostic tests to ascertain if you have a faulty door switch.
5. Faulty Hood Switch
Hood switch issues are a common cause of nuisance alarms. Also known as the hood latch sensor, this component is in charge of detecting the position or status of the vehicle’s hood (shut or open).
It is a simple mechanism – if the hood is “open” when the alarm is armed, then this will trigger the alarm.
However, if the hood switch is faulty it can send the incorrect signal to the car’s computer thus triggering the alarm.
Despite the relative simplicity of the hood switch, problems with it may arise due to dirt, grime, wear and tear and even manufacturing errors.
If you are mechanically inclined we suggest giving the hood latch a clean, clean the hood latch sensor and ensure the connections are tight – if it looks damaged you can buy and fit a new switch.
Alternatively, a trip to the dealer or your local mechanic is the easiest option.
One owner on FixYa.com responded with this advice to a 05 Trailblazer owner who was struggling with an alarm that goes off and wouldn’t shut off:
“I had the same problem, the solution was a bad hood switch. The wires behind the switch had bad connections which would cause a false open on the switch, which would sound the alarm.”
6. Aftermarket Alarms
An incorrectly installed or faulty aftermarket alarm system is a common cause of nuisance alarms.
Aftermarket alarms are typically far more complex than any factory-installed equipment which makes them more prone to issues.
They may also have been installed by incompetent individuals.
If you are experiencing issues with an aftermarket alarm, the best thing to do is speak with a reputable auto electrician.
7. Faulty Body Control Module
A common reason why a Trailblazer 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.
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
8. Damaged Wiring
Damaged electrical wiring can cause a wide range of problems, it can often be tricky to pinpoint too and you may need to have an auto electrician run some diagnostic tests.
9. Animals Climbing On The Vehicle
If your alarm has been set off in the middle of the night, it may have been by an animal climbing on the car.
Have a look for footprints on the hood and the roof.
Check for Recalls or TSBs
By entering your car’s VIN number on Chevrolet’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.
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.
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 Ajar’.
Take it to a Chevrolet Dealership
If needed, take your Chevrolet 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 unit is still under warranty then they should fix and resolve the issue for free.
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.