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Fun with the immobilizer: I took apart a key and removed the immobilizer chip inside to test the range of the antenna.


I thought that it would only activate the antenna if the key was correct which is why I didn't just wave the entire key around the ignition. This is wrong, there are separate measuring fields that says if the key is correct for start and another measuring field if the chip is in range and OK.

As it turns out, the immobilizer is only checked at engine start even though it's constantly being monitored. I left the bare metal key in the ignition and engine running and removed the chip - the engine still ran fine for about a minute even though the car knew that the chip signal was gone. I'm assuming that it would continue to run because I'm not going to drive around on public roads with possible risk of the engine shutting down.

Range of a chip in the key is about 1" so if you have a code related to low signal there's no way pushing the key or wiggling it will make the signal stronger. If it does, there was a problem with with the antenna or plug, not the key range. The chip has more than enough range. Outside of the key, a naked chip has about 3" of range.

Holding a VW chip from another car right at the antenna also has no effect. The car knew that a correct chip was in range even though an incorrect chip was also in range. The tested car was a mk5 with immo4 and the incorrect key was a mk4 with immo3, I don't know if this could have made a difference.

In any case, even if you have another compatible immobilizer chip in your pocket, unless you're holding it right up against the ignition slot, it's not going to be read.

More information on the immobilizer: http://www.myturbodiesel.com/1000q_how_to/multi/immobilizer.htm
 

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Cool trick. I'm glad they didn't set it up so the engine shuts off if the signal blinks out for a second!

FYI, these are the same types of tags that are put into pets for lost pet ID.
 

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Well, I tried putting another immobilizer chip from the same generation car and immobilizer right up against the antenna while using my normal key. No problems starting, no error messages. The incorrect chip was closer to the antenna than the correct key since it was naked (not in a key) and pressed right up against the ignition slot.
 

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Probably work the same way as keyless ignition

The immobilizer probably work the same way as those keyless ignition offered by other companies, such as Mazda. I've test drove a Mazda Miata before. The dealer demonstrated the keyless ignition. You can just leave the key in your pocket, and the engine will start as long as you're in some sort of close vicinity.

I asked, what if you start the car, then get out of the car and let another person drive away without the key? The dealer said, yeah, they can drive away as far as they want, but they better not stop the car -- since they won't be able to start the car again.
 

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The immobilizer probably work the same way as those keyless ignition offered by other companies, such as Mazda. I've test drove a Mazda Miata before. The dealer demonstrated the keyless ignition. You can just leave the key in your pocket, and the engine will start as long as you're in some sort of close vicinity.

I asked, what if you start the car, then get out of the car and let another person drive away without the key? The dealer said, yeah, they can drive away as far as they want, but they better not stop the car -- since they won't be able to start the car again.
What if you drop the key in between the seats and can't find it? The doors will be unlocked and the start button active. I'll be Mazda also has a tool to get around the keyless ignition.
 

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Discussion Starter #7
I think that the chip is very reliable. I'll bet that most are traced to the instrument cluster, wiring, or antenna in the ignition cylinder.
 

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When I read about someone who has a random immobilizer problem, what's the cause? Can this chip have failures?
Probably not the chip. I've heard of the antenna failing a few times. The antenna could also have a plug or wiring problem. The instrument cluster is pretty reliable too.
 
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