Simple Functional Test for Mercedes Infra-red Remote Keys


Sometimes it may be necessary to prove an older style Mercedes Benz infra-red key is working.  At least to prove the batteries are functioning and that the key is emitting and infra-red beam before further diagnostics are carried out.

Mercedes infra red key test

Mercedes Infra-red key remote

Mercedes infra red key test

Mercedes Infra-red key remote – IR window


Using either a mobile phone camera or digital camera to carry out this simple quick test that allows you to at least prove the most basic function of your IR remote key.

Position the key so you can view its red IR window on the screen of your phone or camera, press the operating button on the key and observe the image on the device.  Due to the optical filtering in the camera (CCD) you should be able to see the invisible infra-red light illuminating in a blue-grey point of light.  This cannot normally be seen with the naked eye, but once viewed through a camera or camera phone it can easily prove that there is IR light being emitted from your remote – If not check the batteries!  This simple trick can be used on all IR remotes, home TV, HiFi etc.

Mercedes Infra Red remote key testing

No IR light emitted – as viewed through camera/camera phone


IR Light emitted – as viewed through camera/camera phone

It is worth remembering that this is a really basic test. The battery actually needs to have more power than is needed just to illuminate the LED to correctly operate the immobiliser and locking system.  You will often get an indication on the rear view mirror warning of failing batteries in the remote.  This warning will be indicated to the driver on activation of the key fob, by alternate flashing of both the red and green mirror status lamps for a brief period.  Whilst the locking and unlocking will be unhindered and still function as it should, it is warning that the fob batteries are in need of replacement and should be changed as soon as possible.


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