Is it possible that an immobilizer has malfunctioned to the point where the adding-new-fobs process doesn't work, but the actual immobilizer is still working? Or is it more likely I'm doing something wrong?


I've got a '93 Toyota MR2 with a factory alarm, and after-market immobilizer. The immobilizer is about 18 years old. I've owned the car for a few months, and when I bought it, it had one master key fob, and one user fob.

I wanted to wipe the old user fob and re-add it, to ensure no previous owners could disable the immobilizer, so I followed the instructions from the original booklet for the immobilizer. This involved opening doors and turning the ignition on/off in sequence. After a while of trying, I couldn't get the dashboard LED to react in the way the booklet said it should, or even do anything different from it's normal flashing sequence when it's arming and disarming. I gave up for the day.

However, I then noticed that the original user fob was no longer working - I'd obviously got far enough through the process to wipe all old fobs. The immobilizer still works, in that you have to present the master fob in order to start the car. However, I still can't get it to program any new ones.

As an added bonus, since doing this, the alarm now resets itself if you close the doors for more than a minute or so without putting the key in the ignition and disabling the immobilizer. It's possible that this was an issue beforehand, but I first noticed it while trying to re-add the fob, and it does it quite frequently now.

  • 3
    Do you know what manufacturer made the aftermarket immobilizer? If they are still trading I'd be tempted to contact their technical team as a first port of call. Commented Jul 15, 2015 at 10:05
  • It's a Sigma SG80, and I don't think the manufacturer is still going (although apparently Sterling key fobs should work with it, so not sure if the company just changed names or was bought at some point).
    – Dan
    Commented Jul 15, 2015 at 18:10

1 Answer 1


With very old aftermarket electronics the only real thing that can be done is removing the system. With aftermarket electronics there is little to no support, no replacement parts and no predictable failure mode.

Before you drive your self insane or get stranded somewhere when the system fails altogether, remove the immobilizer system.

  • Couldn't agree with you more. Sound advice. Commented Jan 21, 2016 at 0:29

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