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Hi I’m new here but I have owned my IS300 for 12 years. I do most of the the mechanical work myself. I would like to ask if anyone knows anything about the anti theft system and how to reset it. Just before Christmas I replaced the thermostat and fitted new Battery terminals I left the Battery off of the car until I had finished the thermostat.When I refitted the Battery the car refuses to start turns over but will not fire. I have noticed that the security light flashes after the car is unlocked and only stops when the ignition key is inserted.When the car is locked and I have opened the door with the keys and not the key fob the alarm does not go off.Has anyone experienced this problem.I have seen the dodgy videos on YouTube but I am reluctant to take their advice.


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Security light should continue to flash until the key is in the barrel. This indicates the immobiliser is active until the key is brought in close proximity to the sensor which is right next to the barrel.

The fact that the light stops flashing indicates the immobiliser is being disabled and therefore isn't the cause of the engine not firing.

I would check all the fuses in the engine bay, including the large high amp ones - I've known some to blow when people change the Battery, especially if the Battery was accidentally connected the wrong way round (which normally blows the 120A fuse module and is a pain to replace (bolted in from the underside of the fusebox)).

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Yes that's a good point. I think there are a couple of electrical connectors and wiring close to the thermostat - and I think one of them is the crank sensor which would certainly stop the engine from firing if that were disconnected.

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