Allready in the start up screen module comm error what is that

That is a communication code between modules. One module has probably dropped its Can Bus signal. The part may still work but it wont be efficient. Usually it will require the dealer to access the his COMM line thru their tester. OBD 2 does not cover S codes.

Sigh...there can be alot involved in NO COMM faults. Do the instrument warning lamps come on with the key as normal? Do they all go to self test modes when turning to start? Most GM products either have a dedicated fuse for DLC or use the Radio fuse. If you have a meter or a testlight, pin 16 (Looking at the DLC, top side is the wider of the 2 sides, bottom.narrow side furthest right is pin 16) will be the 12v power port. If you can test for power there, and you dont have it, you have a broken wire or a blown fuse or a bad connection most likely, or possible ignition switch issue.
If you DO have power (Minimum 10.5v to be sure it will connect), then it becomes more involved. You need to start checking grounds as well (DLC Pins 4 and 5. Top left is pin 1, count to the right) and then checking modules directly for power and ground or checking comm lines at the can buss connector. This really requires a system diagram for all modules connected on the comm buss, and a wiring diagram to know which wires you will be testing, plus its worlds easier if you have an enhanced scantool capable of talking to all modules on the vehicle. If no modukes can communicate, then you can backtrack from your DLC till you find where there is no signal, but that could take awhile. However if some communicate and others do not (Your car probably has 15 modules that can comm) then it can really speed up the process because you will then know where the fault ISNT, and can narrow down the search for locations.
Having seen a few GM systems get upset with water intrusion, or individual modules pulling down the buss, you could try disconnecting the ABS module connector and rechecking comm. I have seen loose plugs on that, as well as burned out ABS modules cause NO COMM. I only start there because its usually easy to unplug and test the ABS.
Aside from that, you really will need test equipment and accurate diagrams to properly proceed. But with any luck, the power and ground testing may get you going. Id start there if it were at my shop, and proceed to scan tests and buss wiring checks next.

This is Error 205 details if it helps,
105. (01101001) Comms Error Time Out
These faults are reported when the Display Module detects an error in the communications between the Display Module and the Motor Control Module.
Primary Source: Display Module.
Action: Replace Display Module.
Secondary Source: Motor Control Module.
Action: Replace Motor Control Module.
Tertiary Source: Rotor Position Sensor
Action: Replace Rotor position Sensor. If this corrects the fault refit the
original Display Module and/or Motor Control Module.

check body control module

Error Code 105
105. (01101001) Phase 2 to 5 - Comms. Error Time-out
These faults are reported when the Display module detects an error in the communications
between the Display module and the Motor Controller.
NB. If the product is an IW, check that the motor controller is not 426520. If it is replace with a
compatible part. This is incompatible and will give a fault code 105 at the start of agitate. Not
before! If it is a 426520 replace motor controller with a compatible part.
Primary Source - Display module
Action - Replace Display module.
Secondary Source - Motor Controller
Action - Replace Motor Controller
Tertiary Source - Rotor Position Sensor (Phase 5 Only)
Action - Replace Rotor Position Sensor. If the new Rotor Position Sensor corrects the fault refit
the original display module and motor controller.

Try to get a Rotor position sensor as they are cheaper.
105. (01101001) Comms Error Time Out
These faults are reported when the Display Module detects an error in the communications
between the Display Module and the Motor Control Module.
Primary Source: Display Module.
Action: Replace Display Module.
Secondary Source: Motor Control Module.
Action: Replace Motor Control Module.
Tertiary Source: Rotor Position Sensor
Action: Replace Rotor position Sensor. If this corrects the fault refit the
original Display Module and/or Motor Control Module.

105. (01101001) Comms Error Time Out
These faults are reported when the Display Module detects an error in the communications
between the Display Module and the Motor Control Module.
Primary Source: Display Module.
Action: Replace Display Module.
Secondary Source: Motor Control Module.
Action: Replace Motor Control Module.
Tertiary Source: Rotor Position Sensor
Action: Replace Rotor position Sensor. If this corrects the fault refit the
original Display Module and/or Motor Control Module.

this will happen if you do have a single com module and the program is set up for 10base ( internet ) com if this is the case you will need a dual com module the first thing the unit does when you run a transaction is to look for the com port is it is 10 base it will look for the internet connection " BUT " if the comm module is bad meaning it took a power surge hit them you have to replace it if you need more help call us @ 775- 358 2922 hope this help : - )

a comm error is an error to the alarm company who is monitoring it.

thats a problem with the d2b fibre optic system more than likely the module wake up call to the d2b modules is missing corroded or bad connection or a faulty module in the ring not passing the message around. think its white/orange wire that goes around the modules.be a good idea to take to a jag dealer the have the correct diagnostic kit to a module comms test