IMMOBILISER
Fault finding – Introduction
OPERATIONAL SPECIFICATIONS
The immobliser system is based on the recognition of a key by the inductive connection between the transponder built into the key and the transponder loop aerial every time starting is requested.
The key is authenticated when the transponder aerial detects the correct code, when the vehicle is in the protected status (immobiliser active).
After each switch-off of the ignition, the immobiliser is automatically activated after a delay of 10 seconds.
NOTE: for Belgium, the delay is one second.
OPERATION
– In this mode, transponder authentication is initiated by the transponder aerial detecting the key (+ After ignition).
– When the user puts his key into the ignition switch and switches on, the UCH asks for the key number via the transponder ring.
– In response to this request, the key gives its unique number to the UCH.
– If this response is recognised by the UCH (meaning that the key has been programmed into the UCH), the UCH sends the key a message (challenge).
– The key deciphers the message. If the message is recognised, the key sends back its response.
The UCH compares the response with the value stored in its memory.
If this response is recognized by the UCH, then the authentication is successful.
All data exchanged between the key and the UCH is encrypted.
– Once key authentication is successful, the UCH authorises operation of the engine management computer (exchange of an immobiliser code with the injection computer).
Recognition of keys in normal operation
-vehicle protected (without After Ignition) = indicator light flashes at 1 Hertz
-key recognised, injection system unprotected = warning light comes on constantly for 3 seconds then
goes out
-key recognised, injection system protected or blank = warning light remains lit after 3 seconds
-key not recognised = warning light flashes at 4 Hertz.
From service book.
Here I hope this helps you. Good luck.
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