Immobilizer Anti-Theft System Description; Electronically Coded Keys; Detection Coil; Immobilizer Control Unit - Daewoo Nubira Owner's Manual

9T – 10IIMMOBILIZER ANTI–THEFT SYSTEM
GENERAL DESCRIPTION
AND SYSTEM OPERATION
IMMOBILIZER SYSTEM
The purpose of the immobilizer system is to prevent the
vehicle from being stolen or driven by unauthorized users.
Users are authorized by an electronically coded key.
When the ignition is turned ON, the key is tested by the im-
mobilizer system. While the key code is being read by the
immobilizer control unit, the engine can start and run with
any key that will turn the lock cylinder. The key code is read
and compared with key codes that have been stored in the
immobilizer control unit's memory.
If a valid key is detected, the immobilizer control unit sends
a serial data release message to the powertrain control
module (PCM)/engine control module (ECM). Included in
the release message is an identification (ID) code which
assures that neither the immobilizer control unit nor the
PCM/ECM has been substituted to defeat the system.
If the PCM/ECM does not receive a release message with-
in a specified time, or if the ID codes do not match, the
PCM/ECM performs the following actions:
S
Disables the fuel injector circuit.
S
Disables the fuel pump circuit.
S
Disables the ignition coil.
S
Sets diagnostic trouble code (DTC) 53.
The above conditions are maintained until the ignition is
turned OFF.
The immobilizer control unit system consists of the follow-
ing components:
S

Electronically coded keys.

S

Detection coil.

S

Immobilizer control unit.

S
PCM/ECM.
S
Instrument cluster indicator.
S
A data link connector (DLC) to provide serial data
access for a scan tool.
A PCM/ECM for a vehicle without an immobilizer control
unit cannot be interchanged with a PCM/ECM that is used
with an immobilizer control unit system. The immobilizer
control unit and the PCM/ECM must have a matching ID
code. ID coding and key coding are accomplished by using
a scan tool.
ELECTRONICALLY CODED KEYS
Each valid ignition key has an internal transponder which
transmits a unique code. When a key is inserted into the
ignition lock, the transponder is inductively coupled to the
detection coil. The transponder interacts with the detec-
tion coil to generate an amplitude modulated modulated
signal which is conducted from the detection coil to the im-
mobilizer control unit. The immobilizer control unit reads
the radio–frequency signal. A release message is sent to
the powertrain control module (PCM)/engine control mod-
ule (ECM) if the key is authorized.
New keys are coded by using a scan tool. Refer to in this
section."Key Coding Procedure"
DETECTION COIL
A detection coil is mounted at the ignition lock as an inte-
gral part of the key position trim ring. The wires to and from
the detection coil are connected to the immobilizer. When
the ignition is turned ON, the immobilizer energizes the
detection coil and the coil is coupled inductively to the
transponder in the ignition key. The immobilizer sends a
modulated signal to the detection coil. The signal is
changed by interaction with the internal transponder in the
ignition key. The immobilizer reads the signal from the
detection coil and determines whether the key is autho-
rized.
IMMOBILIZER CONTROL UNIT
The immobilizer control unit is an electronic module in the
instrument panel which verifies the validity of an ignition
key when the ignition is turned ON.
To accomplish its purpose, the immobilizer control unit
performs the following actions:
S
Learns and stores the codes of valid keys.
S
Reads the radio frequency input from the ignition
key.
S
Compares the received code with the codes of the
valid keys.
S
Sends a release message to the powertrain control
module (PCM)/engine control module (ECM) if a
valid key has been presented.
S
Calculates and transmits identification (ID) codes
within each release message.
S
Controls the external relay which interrupts the
starter relay circuit.
S
Controls the status indicator in the instrument clus-
ter.
S
Monitors system faults.
S
Supports system test functions.
Normal Operation
When the ignition is turned ON, the immobilizer control
unit tries to read the key code transmitted by the trans-
ponder in the ignition key.
If a valid key is detected, the immobilizer control unit sends
a release message to the PCM/ECM. The release mes-
sage contains an ID code. Immobilization will be per-
formed by the PCM/ECM if no release message is re-
ceived, or if the ID code in the PCM/ECM does not match
the immobilizer control unit ID code.
If a non–valid key is detected, the release message is not
sent to the PCM/ECM.
When the driver turns the ignition OFF, the immobilizer
control unit switches to the active mode.
DAEWOO V–121 BL4