Start prevented, try again

[maleekberry]

I took my car to my mechanic to get the radio checked but after trying to trace what the might be, the car refused to start, it doesn't even crank, it says start prevented, try again and when diagnosed it says "ECM 720A, immobilizer communication missing" this car has been there for 3 weeks now and counting and no one seem to have a solution to it, the last guy said I should buy an entire new ECU, immobilizer and key which he doesn't have a programmer to program it, please help me out here I'm actually out of options on what to do. It's a Volvo S60 2004 model

[RickHaleParker]

It is a communication problem. Good chance the mechanic knocked a communication cable loose when digging around.

Check the wiring and reset the immobilizer by locking/unlocking the door 5 times in a row with the remote or the key.

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ECM-720A Immobilizer communication. Faulty signal. Permanent fault

Diagnostic trouble code (DTC) information

Condition
The engine control module (ECM) contains a code for the immobilizer which is unique to each car. Before the engine can be started, the immobilizer code is checked to ensure that it corresponds to the central electronic module (CEM) and the engine control module (ECM). Diagnostic trouble code (DTC) ECM-720A, faulty signal, will be stored if the code for the immobilizer does not match.
Diagnostic trouble code (DTC) ECM-720A, signal missing, will be stored if there is no communication between the central electronic module (CEM) and the engine control module (ECM) so that the immobilizer code cannot be checked.
The fault is diagnosed by the engine control module (ECM) when the ignition is switched on.

Substitute value
none

Possible source
Faulty signal:

• the engine control module (ECM) is not programmed and has no immobilizer code
  the immobilizer code in the engine control module (ECM) is incorrect
  the immobilizer code in the central electronic module (CEM) is incorrect
  the central electronic module (CEM) is not programmed and has no immobilizer code
  the central electronic module (CEM) is defective
  the engine control module (ECM) is defective.

Signal missing:

• open-circuit in the communication between the central electronic module (CEM) and the engine control module (ECM).

Fault symptoms
the engine does not start.

[maleekberry]

Already did the lock/unlock thing weeks ago but nothing still, I just believe if a right programmer can be used it should be fine, the ish is I don't know which programmer will work so I ask for around for a mechanic that might have or if there's another solution please I'm all ears