Design
Design
General
The security system in the vehicle is a distributed system which is monitored by the central electronic module (CEM). A number of other units and components are involved for the various functions.
Central electronic module (CEM)
The central electronic module (CEM) (4/56) is the master unit for the immobilizer. The central electronic module (CEM), steering column lock module (SCL) and the engine control module (ECM) are linked by codes. The central electronic module (CEM) is also programmed with codes for each ignition key that belongs to the vehicle.
If the vehicle has an alcolock (option 2009-) installed, the code in the handset unit must also be programmed into the Central electronic module (CEM) to work. The signal from the alcolock handset is received by the Remote Receiver Module (RRX), which forwards the signal to the Central electronic module (CEM).
Note! The steering column lock module (SCL) is only available on model year 2004-2008 for the USA/CDN market and model year 2004- for other markets.
The central electronic module (CEM) transits commands and signals to the other control modules included in the system. The identity of the key is checked by the central electronic module (CEM) via the start control module (SCU). In cars with the keyless entry locking system the identity of the key may also be checked by the keyless vehicle module (KVM) via the antennas. The control module which validates the key depends on whether the vehicle is being started passively or not. There is a communication circuit in the ignition key, known as a transponder. The transponder has a unique identification code that must be learned by the central electronic module (CEM) before the key can be used to start the vehicle. This learning process takes place during installation at the factory. New keys can be added afterwards.
If there is a keyless vehicle module (KVM) installed in the vehicle, the central electronic module (CEM) requests that it checks the identity of the key when the starter button is pressed.
The central electronic module (CEM) checks the relay for the fuel pump (FP). When the identity of the key and all included components have been checked, the central electronic module (CEM) activates the fuel pump (FP) after a command from the engine control module (ECM).
For further information about the central electronic module (CEM), see Design and Function, central electronic module (CEM).
Keyless vehicle module (KVM) (only vehicles with the keyless locking system)
The keyless vehicle module (KVM) controls the keyless functions in the vehicle. The keyless vehicle module (KVM) works together with the central electronic module (CEM) when checking the key identity. For further information, see Design and Function, keyless vehicle module (KVM).
Start control module (SCU)
The start control module (SCU) (3/1) is in the dashboard beside the steering wheel. The start control module (SCU) contains a cylinder for the key, an antenna ring and four contact breakers. There is one contact breaker for each of the three key positions (I-III) and one to indicate that the key is in the ignition switch.
The contact breaker for key in is designated Key-in contact breaker. The key-in contact breaker closes when the key is inserted in the ignition and indicates to the central electronic module (CEM) that the car is about to be started.
The antenna ring is activated by the central electronic module (CEM) when the signal from the key-in contact breaker has been received. The antenna ring allows the central electronic module (CEM) to communicate with the transponder in the ignition key.
The key does not need to be in the ignition switch if there is a keyless vehicle module (KVM) in the vehicle. There is a starter button instead. The starter button must be pressed in before it can be turned from position 0 to I. This activates the key-in switch. The identity of the key is then checked via the antennas in the passenger compartment instead. These antennas are connected to the keyless vehicle module (KVM).
Alcolock (option 2009-)
See Design and Function, Alcohol Analysing Start Inhibitor.
Steering column lock module (SCL)
Note! The steering column lock module (SCL) is only available on model year 2004-2008 for the USA/CDN market and model year 2004- for other markets.
The steering column lock module (SCL) (4/102) checks the function of the steering wheel lock. The control module is underneath the steering column inside the passenger compartment. The steering column lock module (SCL) is directly connected to the central electronic module (CEM). The central electronic module (CEM) transmits commands to the steering column lock module (SCL) when the steering lock needs to be locked or unlocked. The communication between the steering column lock module (SCL) and the central electronic module (CEM) is encrypted. Codes for the immobilizer function must be downloaded before the steering column lock module (SCL) can work in the vehicle. This takes place when downloading software.
The steering column lock module (SCL) consists of:
- an electric motor
- a spring bolt
- a communication circuit
- a switch.
The steering column lock module (SCL) locks the steering wheel using the spring bolt. The spring bolt is moved back and forth by the electrical motor. The position of the spring bolt is indicated by the contact breaker in the steering column lock. The steering column lock module (SCL) transmits information at regular intervals about the position of the spring bolt to the central electronic module (CEM). A diagnostic trouble code (DTC) is stored in the central electronic module (CEM) if the spring bolt cannot be unlocked or its position cannot be determined. A message will also be shown in the display on the driver information module (DIM).
Hint: If the steering wheel is loaded when trying to unlock the steering wheel lock, the motor for the lock may be unable to unlock it (too much pressure on the spring bolt). An error message will be shown in the display on the driver information module (DIM) if this is the case. If this should happen, move the steering wheel slightly to reduce the pressure on the spring bolt, remove the ignition key and then re-insert it.
The steering column lock module (SCL) is powered and grounded by the central electronic module (CEM).
Engine control module (ECM)
The engine control module (ECM) (4/46) checks the relay for the starter motor and the ignition system. The logic for the start inhibition system is also in the engine control module (ECM). The engine control module (ECM) also transmits a command to the central electronic module (CEM) indicating when the fuel pump (FP) can be activated. The functions are activated after:
- the ignition key has been approved
- the steering column lock is unlocked
- the communication check has been run with the central electronic module (CEM) and the brake control module (BCM).
The engine control module (ECM) must be programmed with codes before it can work in the immobilizer system. This takes place for the first time during assembly in the factory, and subsequently takes place in the event the control module is replaced (when downloading software)
As a further safety precaution, the engine control module (ECM) reads off the serial number from the brake control module (BCM). These numbers are compared with the number programmed into the engine control module (ECM). The engine will not start if the numbers do not correspond. This means that these numbers must be programmed into the engine control module (ECM) if it or the brake control module (BCM) has been replaced. This takes place automatically when downloading software.
The engine control module (ECM) transmits the status of the engine (whether it is running or not) on the controller area network (CAN). The central electronic module (CEM) uses this signal together with the signals from the brake control module (BCM) and transmission control module (TCM) to determine whether the steering wheel lock can be locked or not. For further information, see Design and Function, engine control module (ECM).
Brake control module (BCM)
The brake control module (BCM) (4/16) transmits signals on the controller area network (CAN) about the vehicle speed. The central electronic module (CEM) uses this signal or the corresponding signal from the transmission control module (TCM) to determine whether the vehicle is moving. The central electronic module (CEM) uses these signals together with the signals from the brake control module (BCM) and transmission control module (TCM) to determine whether the steering wheel lock can be locked or not.
When deactivating the immobilizer system, the communication between the engine control module (ECM) and brake control module (BCM) is checked. During this check, the engine control module (ECM) reads off the serial number from the brake control module (BCM) and compares this with a number it has programmed. The engine will not start if the numbers do not correspond.
For further information, see Design and Function, brake control module (BCM).
Transmission control module (TCM)
The transmission control module (TCM) (4/28) transmits signals on the controller area network (CAN) about the vehicle speed. The central electronic module (CEM) uses this signal or the corresponding signal from the brake control module (BCM) to determine whether the vehicle is moving. The central electronic module (CEM) uses these signals together with the signals from the brake control module (BCM) and transmission control module (TCM) to determine whether the steering wheel lock can be locked or not.
For further information, see Design and Function, transmission control module (TCM).
Driver information module (DIM)
The driver information module (DIM) (5/1) receives information from the central electronic module (CEM) about which message is to appear in the display. A message will be displayed if there is a fault in any of the checks run by the system.
For further information, see Design and Function, driver information module (DIM).