L322 Range Rover System Description and Operation
SECURITY
DESCRIPTION AND OPERATION 86-5-13
Immobilisation System
The immobilisation system is a transparent system that prevents unauthorised starting of the vehicle by providing a
secure interface between the ignition switch and the Engine Control Module (ECM). It also prevents the engine from
starting if the steering lock is engaged or if the gearbox is not in park or neutral.
The immobilisation system consists of:
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The transponder in each ignition key
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The transponder coil around the ignition switch
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The immobilisation ECU.
Transponder
A transponder, consisting of a wireless Electronic Erasable Programmable Read Only Memory (EEPROM), is
incorporated into the head of each ignition key, including the 'wallet' ignition key. A password and key code in the
transponder provides each ignition key with a unique identification. As a further security measure, the transponder
contains a rolling code number written to it from the immobilisation ECU. The transponder key code and rolling code
are entirely separate from the remote handset codes.
The transponder is written to and read from by the immobilisation ECU via the transponder coil. The maximum range
for communication between the transponder and the transponder coil is approximately 20 mm (0.8 in).
Transponder Coil
The transponder coil is installed around the top of the ignition switch key barrel to enable communication between the
immobilisation ECU and the ignition key transponder. To operate the transponder the immobilisation ECU energises
the transponder coil with a 125 kHz ac current. This energises the transponder by electromagnetic induction.
Amplitude modulation is used to write data to the transponder.
CAUTION: The drive for the transponder coil is not capable of carrying battery voltage and care must be taken
when fault finding and probing the system otherwise permanent damage to the immobilisation ECU may
result.
Immobilisation ECU
The immobilisation ECU is installed on the driver's side of the gear selector assembly, underneath the centre console.
When it detects a valid transponder/ignition key in the ignition switch and is receiving a release signal from the steering
lock ECU, the immobilisation ECU sends a release signal to the ECM and energises the starter solenoid when the
ignition switch is turned to crank. The release signal to the ECM is a further rolling code synchronised in the
immobilisation ECU and the ECM. If either the ECM or the immobilisation ECU are replaced they have to be re-
synchronised using TestBook/T4.
Up to 10 different transponders can be used with the immobilisation ECU. The 10 unique transponder key codes and
their associated rolling codes are generated during vehicle production and programmed into the immobilisation ECU.
The transponder of each ignition key supplied with the vehicle is then programmed with one of the key codes and its
associated rolling code. Once the immobilisation ECU and the transponders have been programmed they cannot be
over written. The 'spare' key codes and associated rolling codes are retained in the immobilisation ECU for future use.
The key codes and associated rolling codes are also recorded in a spares support database together with the Vehicle
Identification Number (VIN).
If an ignition key is lost, the key code of the related transponder should be disabled in the immobilisation ECU using
TestBook/T4. If the key is subsequently found, the transponder can be enabled again.
If a replacement or additional ignition key is ordered, the transponder of the new ignition key is programmed by the
spares supplier with one of the spare key codes and associated rolling code from the spares support database. The
immobilisation ECU recognizes the first use of the key code and automatically enables the new ignition key.
When a replacement immobilisation ECU is ordered it comes pre-programmed with the key codes and rolling codes
from the spares support database ready for use with the existing ignition keys once it has been synchronised with the
ECM.
A starter motor protection function is incorporated into immobilisation ECU. When the engine speed exceeds a
predetermined value, a relay inside the immobilisation ECU is disabled. This prevents damage to the starter motor in
the event of a sticking ignition switch or if crank is selected while the engine is running.