Technical Information about immobilizer

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Technical Information about immobilizer

Gialuca76

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Goodmorning to everyone,


my father has a Fiat Punto first series (176) 75 ELX since 1997. A strange thing happened, on Monday we changed the battery (usually the duration is 5 years) so this is the fifth that we change only that after changing it the key code light is fixed on and engine not turn on. We tried with all three keys including emergency starting, but the injector light does not come on. I tried to measure the impedance of the immobilizer antenna and 33.35 ohm.
The problem may be the antenna or i must to change 46734570 electronic control unit?
If i buy a new electronic control unit i need to code the old keys?
Thanks
 
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Changing the battery when there is an immobiliser fitted can be a problem. You should always connect a 'slave' battery in parallel so that the electronic ECU is kept alive while the main battery is being changed. Only when the new battery is correctly hooked up should you disconnect the 'slave' battery. A device is available that plugs into the cigar lighter, and supplies 12v to the system while switched off, this acts as the 'slave' battery although only if the cigar lighter is alive when the ignition switch is 'off'.

For some reason the immobiliser code can get 'forgotten' during the short time the battery is disconnected, although such memory should not be volatile memory for such a purpose, instead should be of the Cmos type which is semi-permanent.

It has happened to me on a Land Rover Discovery, and I had the ECU modified to omit the immobiliser key code check, so it can never happen again.
 
Thanks for the contribution, you will treasure it in the future. Unfortunately the machine is no longer distributed ... Immobilizer antenna changed, control unit replaced with a to which the code was removed but nothing to do:bang:. Eventually I took her to the wrecker.:cry:
 
Half an hour of an auto-electrician's time would almost certainly have fixed your problem. There is a tool available that plugs into the OBD socket of most modern cars that keeps the immobiliser and radio codes freshened while you change the battery.
 
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