RT-3 USER GUIDE____________________________________________________
vehicle by unauthorized people by means of a key recognition electronic system and codified
ECUs.
Ford uses two kind of immobilizer system named PAT I and PAT II, being this last an
improvement of the first one.
7.2.2 OPERATION
There is a dialog through an interconnection channel between the injection ECU and the
immobilizer ECU, to allow or not the vehicles´ ignition. This protection is implemented at
two levels; so, there are two conditions to be fulfilled for the authorization to take place:
1.
The immobilizer´s ECU is programmed to allow the starting only with the previously
right coded injection ECU. This means that in case of replacement of one of the
ECU’s, the immobilizer must be programmed to recognize the new engine ECU.
2.
The immobilizer authorizes to start only if the key’s code has already been stored by
the system ECU. That means that in case the customer needed a new key, this should
be recognized and memorized by the immobilizer.
The steps done by ECU before authorizing the ignition are the following:
The user introduces the key and turns it on. Each key has a chip that emits a code
when excited by a radiofrecuency signal. That signal is emitted from the ignition
lock cylinder when the contact has been done, then, a sensor reads the key’s
emitted code.
Immobilizer´s ECU compares the read code with the stored codes(with a
maximum of 8 with PATS II and 16 with PATS I). If the read code ,matches with
one of the stored codes, the immobilizer´s ECU authorizes the starting. On the
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