2000 Volvo S80 Won, t start sometimes.

I don't believe its is and if so I am not aware of it
what we find very common to effect the system is security passes and electronic sticks
if placed with the key on the same ring
THEORY & OPERATION - C70, S70 & V70 TURBO & S80 -2000 Volvo S80
ENGINE IMMOBILIZER SYSTEM

Immobilzer System
Each engine variant has a unique MIN code. The code is fixed and is programmed into the Engine Control Module (ECM). Each has a unique VIN code. The code is determined and entered into the immobilizer control module when the car is built. VIN code is also stored in the Volvo database.

NOTE: When replacing the immobilizer control module the cars unique VIN codes must always be programmed in. In addition, it programs in the MIN code that the immobilizer will be receiving from the ECM.
When the engine is switched on for the first time copies of the VIN code and MIN code are sent to the ECM and Immobilizer Control Module (ICM) respectively. The ECM then "learns" this code and is then "married" to the code.
A new code, the Immo-VGLA (Volvo anti-theft system) code which is used by the VGLA for the override function, has been developed and must be programmed into the immobilizer control module when replacing (6 digit code).
Immobilizer Function
Each time the ignition is switched on the ECM generates a random code (the code is changed every time the engine starts). The random code is sent together with the MIN code as an encrypted signal to the Immobilizer Control Module (ICM).
The immobilizer control module decrypts the signal and compares the MIN code with the MIN code that it has learned. If the MIN code is correct the ICM generates a random code (the code is changed for each engine start). The random code is sent together with the VIN code as an encrypted signal to the ECM. If the MIN code is faulty the engine starts but then stops.
The immobilizer control module decrypts the signal and compares the VIN code with the VIN code that it has learned. If the VIN code is correct the engine starts, if the code is incorrect the engine starts but then stops.
With the ignition on the key is checked to that it is an approved type, the immobilizer sends the Immo-VGLA code to the VGLA control module. This signal is used together with the override function in the VGLA system.

Replacing ECM/ICM Precautions
When replacing the ECM the VIN code must be erased before the ECM is removed. This is so that the ECM can be tested in case of guarantee claims. The VIN code is erased through the Immobilizer Control Module (ICM) diagnostic. The car PIN code is required for erasure.
When moving/testing the ECM) between cars the VIN code must be erased in both car control modules. The erasing can only be carried out in the original car.

Immobilizer Programming
The necessary codes and software can be obtained from the Volvo database using VADIS, the Volvo factory scan tool.