Immobilizer Control System; General Description; Immobilizer Description And Operation; Schematic And Routing Diagram - Suzuki XL7 2007 Service Manual

10C-1 Immobilizer Control System:

Immobilizer Control System

Immobilizer Description and Operation

The immobilizer system functions are provided by the
theft deterrent module (TDM) and the engine control
module (ECM). When an ignition key is inserted into the
ignition lock cylinder and the ignition is switched ON, the
transponder embedded in the head of the key is
energized by the exciter coil surrounding the ignition lock
cylinder. This exciter coil is part of the TDM. The
energized transponder transmits a signal that contains
its unique value, which is received by the TDM. The
TDM then compares this value to a value stored in
memory. If the values match, the TDM will send the
prerelease password via the serial data circuit to the
ECM. If the transponders unique value is incorrect, the
TDM will send the fuel disable password to the ECM.
When the ECM receives the TDM prerelease password,
the ECM will challenge the password. The ECM sends
this challenge back to the TDM via the serial data circuit.
Both the ECM and TDM perform a calculation on this
challenge. If the calculated response from the TDM
equals the calculation performed by the ECM, the ECM
will allow vehicle starting.
The components of the theft system are as follows:
• Theft deterrent module (TDM)
• Engine control module (ECM)
• Ignition key (Transponder)

• Security indicator

Theft Deterrent Module (TDM)
Vehicles with steering column mounted ignition switches
have the exciter integral with the theft deterrent module
(TDM), which is located within the steering column. The
TDM can learn up to 10 keys (transponder values).
The TDM uses the following inputs: battery voltage,
ignition switched voltage and ground circuit. The theft
deterrent control module uses the following outputs:
password exchange and challenge/response with the
engine control module (ECM).
When an ignition key is inserted into the ignition lock
cylinder and the ignition is switched ON, the transponder
embedded in the head of the key is energized by the
exciter coils surrounding the ignition lock cylinder. The
energized transponder transmits a signal that contains
its unique value, which is received by the TDM. The
TDM then compares this value to the learned key code
stored in memory. The TDM then performs one of the
following functions:

Immobilizer Schematics

General Description

Schematic and Routing Diagram

• If the transponder value matches the values stored in
the TDM memory, the TDM will send the prerelease
password to the ECM via the serial data circuit.
• If the transponders unique value does not match the
value stored in the TDM, the TDM will send the fuel
disable message to the ECM via the serial data circuit.
• If the TDM is unable to measure the ignition key
transponder value, the TDM will not send any
messages to the ECM.
Engine Control Module (ECM)
When the engine control module (ECM) receives the
theft deterrent module (TDM) prerelease password, the
ECM will challenge the password. The ECM sends this
challenge back to the TDM via the serial data circuit.
Both the ECM and TDM perform a calculation on this
challenge. If the calculated response from the TDM
equals the calculation performed by the ECM, the ECM
will allow vehicle starting.
The ECM will disable vehicle starting if any of the
following conditions occur:
• The prerelease password is invalid.
• The fuel disable password is sent by the TDM.
• No passwords are received—There is no
communication with the TDM.
• The TDM calculated response to the challenge does
not equal the calculation performed by the ECM.
The Ignition Key (Transponder)
The ignition key for Passkey III+ (PK3+) equipped
vehicles is a standard ignition key with a transponder
located in the plastic head of the key. The transponder
value is fixed and unable to be changed. The
immobilizer system uses the ignition key transponder
value to determine if a valid ignition key is being used to
start the vehicle. There are approximately 3 trillion
possible transponder values. There are no visible
electrical contacts. The keys are identified by + symbol
in a circle stamped into the steel shank of the key.
Security Indicator
The theft deterrent module (TDM) can command the
instrument panel cluster (IPC) to illuminate the security
indicator only when the ignition key is in the ON position.
The TDM will command the security indicator be
illuminated any time a fault is noted in the immobilizer
system and when the engine starting is disabled.