Fix Bosch Alarm Output Trouble Fault Fast

The ‘Output Trouble’ fault on the Bosch alarm warns you that your external siren, smoke detector or strobe light are not working.

Your system may have other outputs however the siren and strobe are the ones that fail most often.

The great thing about the Bosch alarm is that it is constantly testing all the important parts of your alarm. If it detects a malfunction, it alerts you by making the codepad beep.

All you need to do is follow some simple steps and you’ll have your system back to normal in no time!

The first thing to do is work out which of the 3 outputs is faulty. Follow this procedure to test each output individually.

Bosch Output Trouble Quick Fix

1 –Test Output 1 – External Sirens:

Press and hold the 1 key on your codepad til you hear 2 beeps. The external siren will sound for 2 seconds.

If the siren sounded, then Output 1 is working.

If the siren didn’t sound go to the trouble shooting section

2 – Test Output 2 – Smoke Detectors (only applicable if you have a smoke detector connected to your Bosch alarm panel)

Press and hold the ‘Test’ button on your smoke detector. Remember this only applies to smoke detectors connected to the alarm system.

The smoke detector buzzer AND the external siren of your alarm system should operate within 15 seconds.

If they did, Output 2 is working. If not, go to the troubleshooting section below.

3 – Test Output 3 – Strobe light:

Press and hold the 3 key for 3 seconds. This turns the strobe light on.

Head outside and check that the light is flashing.

If it is, Output 3 is working.

Press and hold the 3 key again to switch the strobe off.

4 – Test Output 4 – Internal sirens:

Press and hold the 2 key on your codepad for til 2 beeps sound.

The internal sirens will sound for 2 seconds.

If they did, output 4 is working.

If not head to the trouble shooting section

Trouble Shooting Output Faults

WARNING: If the battery in your Bosch alarm is not connected, or it’s faulty, the outputs won’t work.

External Siren:

If the external siren failed the most likely cause is a damaged cable between the alarm panel and the external siren.

I’ve written an article here that shows you the best way to repair this kind of fault.

If you’re reasonably handy and have some basic tools, you can easily fix this problem yourself quickly.

Smoke Detector:

This could be caused by:

  • a faulty smoke detector
  • a damaged cable between the Bosch alarm panel and the smoke detector
  • a fault inside the alarm panel itself although this is the least likely reason.

Trouble shooting this fault is best done with a multi-meter. If you feel you’re getting out of your depth here, I would recommend you contact a licensed alarm technician to sort this one out for you.

The basic steps are:

Un-clip the smoke detector from its mounting bracket

Leave all wires connected.

Set the meter for DC volts and look for 12 – 14 volts DC on the red and black wires

If you have the right voltage here that means the output is working correctly, the red and black wires inside cable going to the alarm panel are OK.

If there is no voltage here, either:

  • the cable between the smoke detector and alarm panel is faulty, or
  • there is a fault or programming problem in the Bosch alarm panel.

Assuming you had voltage on Now lets test the other two wires in the cable (I’ll assume they are blue and white, but they could be any color).

Disconnect the blue wire. Momentarily touch it on the white wire. Did the siren start? Good. This means all the wires inside your 4 core cable running back to the alarm panel are OK. The fault will be a faulty smoke detector. Replace it with a new one of the same type and you’ll be all set.

If the sirens did not sound, its time to contact a licensed alarm technician. At least you tried!

Strobe Light:

Again there are only 3 reasons the strobe light wont be working:

the strobe light is faulty

the alarm panel is faulty

the wire connecting the strobe light to the alarm panel is damages or broken

If you want to have a go at fixing this yourself, I recommend you follow this guide on fixing the outside siren. The process is identical.

Internal Siren

The internal sirens are not actually monitored by the Bosch output trouble monitor.

So even if your internal sirens are not working, that will not be the reason for you’re Output Trouble condition.

That said, if they are not working, try this.

Open the lid of the Bosch alarm panel

Find the 3 relay connections on the terminal block – they’re labelled NC, C and NO.

You should have a wire( or possible 2 wires ) in the NO terminal.

Carefully remove the wire from the NO terminal and briefly connect it to the terminal labelled C – its the one immediately to the left of the NO terminal.

Did the internal siren sound?

If yes, there is a wiring fault inside the alarm panel.

If not, the most likely cause is:

  • the cable between the internal siren and the alarm panel is damaged
  • the internal siren itself is faulty.

To fix the wiring problem:

  1. Carefully connect the red or positive wire from your internal siren to the +12 V terminal at the end of the terminal strip – it’s the very last terminal.
  2. Connect the black or negative wire from your internal siren to the NO terminal
  3. Connect a short piece of wire between the C terminal and the GND terminal (located to the left of the +12V terminal.

Now press and hold the 2 key on the codepad until you hear beeps. The internal sirens will sound for 2 seconds.

If they did, well done.

If not, contact a licensed alarm technician to look into the problem for you. The internal sirens are the most effective way to drive a burglar out of your home or office quickly. It’s important that they are working so it will be money well spent.


The outputs (sirens and strobes) are what lets the intruder know he’s been detected.

The Bosch panel constantly monitors these outputs and immediately alerts you if one or more outputs have failed.

Don’t ignore these warnings. My advise is the get the system fixed as soon as possible.

Using this guide you can pin point exactly which output is faulty. You also stand a good chance of being able to fix many of the problems yourself.

If you get stuck contact your friendly licensed alarm technician for help.

Need More Help?

For a short time I’m trialling a one-on-one 15 minute phone consultation service to talk you through any programming settings you’re having trouble with or if you feel more comfortable having a experienced and licensed technician talking you through the programming process.

A call costs $30.00 (FAR less than a service call by an alarm company.)

You’ll get to ask any questions you like and I’ll guide you through the steps to get the result you want.

Lodge a ticket here .

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