How it works.

[loelly]

HI,
My V40 refuses to start now and than.At that moment I can see the crossed out car icon lights up.
Now I try to understand how the immobilizer works.
Suppose It works as follows: Key sends a signal that is picked up by the antenna around the contact. If it is the right key the immobilizer recieves the right code and sends a OK code to the cpu witch release the starting relay ant the motor crancks.Am i right?
If I want to change the immobilizer but keep the key and antenna does this work?

[Clan]

Originally Posted by loelly

HI,
My V40 refuses to start now and than.At that moment I can see the crossed out car icon lights up.
Now I try to understand how the immobilizer works.
Suppose It works as follows: Key sends a signal that is picked up by the antenna around the contact. If it is the right key the immobilizer recieves the right code and sends a OK code to the cpu witch release the starting relay ant the motor crancks.Am i right?
If I want to change the immobilizer but keep the key and antenna does this work?

something like that yes , but first change the antenna ring around the ignition switch , and if it still plays up replace the wiring terminals on the Immobilser unit plug. I believe if you change the immobiliser now you may have to get 2 new keys to go with it ...

[SwissXC90]

Originally Posted by loelly

HI,
My V40 refuses to start now and than.At that moment I can see the crossed out car icon lights up.
Now I try to understand how the immobilizer works.
Suppose It works as follows: Key sends a signal that is picked up by the antenna around the contact. If it is the right key the immobilizer recieves the right code and sends a OK code to the cpu witch release the starting relay ant the motor crancks.Am i right?
If I want to change the immobilizer but keep the key and antenna does this work?

Close but not quite. The ring antenna sends a signal to the key transponder, powering it up. The transponder sends a serial number to the ring antenna. The ring antenna sends the serial number bet to the cem and the ecm. If the serial number is registered, and engine start is permitted.

The car knows what key is permitted to be used. New keys can only be added by Volvo. Second hand keys cannot work.

You cannot change immobiliser and keep same keys.

[loelly]

Where is the serial number located cpu or immobiliser?
Is it not so the recieved code in the immobiliser is send to the cpu where it is compared with the code stored there . If it is the right one the engine is allowed to start.
That way the immobiliser only activate the key and sends the recieved key code to the cpu .So you can change this box. If you use an other key the CPU must go with it to start.

[Clan]

Originally Posted by loelly

Where is the serial number located cpu or immobiliser?
Is it not so the recieved code in the immobiliser is send to the cpu where it is compared with the code stored there . If it is the right one the engine is allowed to start.
That way the immobiliser only activate the key and sends the recieved key code to the cpu .So you can change this box. If you use an other key the CPU must go with it to start.

There are two sets of codes . one connects the key to immobiliser , the other connects immobiliser to Engine ECU