Im attempting to remove an alarm/immobilizer

Lots of car alarms are routed through the head unit/stereo. If you removed it, you've interrupted that circuit and even if you properly tied the alarm circuit back in, it may require reprogramming. If that's the case, it's usually an easy procedure to reprogram it with instructions available from the dealer or by simply googling the procedure.

Anti-theft system problem , possibility ! Do you have a security light blinking ? Security Indicator
The security indicator is located in the clock on the top of the instrument panel. The light emitting diode (LED) displays the immobilizer system status. The immobilizer contains the LED driver hardware for direct connection of the LED.
Vehicle Theft Deterrent (VTD) Operation
The immobilizer system design prevents vehicle theft by interrupting the engine operation. The immobilizer system prevents the vehicle from starting. The engine operating functions interrupt if the immobilizer system does not recognize the transponder identification code of the ignition key. The immobilizer system and the content theft deterrent system do not interact. The system includes the following components:
?€¢
The ignition key

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The column-mounted theft deterrent module with integrated antenna

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The transponder

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The engine control module (ECM

It is possible that the car's alarm/immobilizer system is preventing the vehicle from starting. Manufacturers, in an effort to prevent car theft, have the immobilizer activate if the battery circuit is interrupted for more than a certain number of minutes. This keeps car thieves from cutting battery cables to prevent alarm activation. If the battery goes flat-line dead, the same thing can occur. You need a special tool available at a dealer or repair facility to reset the immobilizer.

Would youlike to remove the alarm,its a aftermarket alarm,you got 2 ways of starting it through the engine compartment using the starter solenonoid.Go under the dash (you will have to disconnect the alarm horn) under the dash near the ignition switch you will see where they have bypassed the starter ignition and connected a relay. on the relay is one of your starter wire on the other is the other part of the starter wire remove the relay and establish the connection orginally and you are done.

Its better you reomove the installed alarm you dont have to remove and restore everything just 2 things the ignition that has be interrupted and the factory alarm in the hood just cut the alrm horn wire. For the ignition you will have to go under the console and remove the panel to access where they have interrupted the original wire. Identify the the ignition wires there you will see where they have splice a wire to a relay match thhe colors that they interrupted and restore that wire (its a 4 wire relay) use a but connection and ensure it does not fall apart start the car if the alarm horn goes off just cut it(NOT the car horn)

toyota has 3 bulletins concerning this vehicle with the same problem,
1 water infuse box and connectors building corrosion this square fuse box in the engine compartment right side, also in that side the wires that et inside the cabin get damage by rodents.

2 immobilizer ecu damage by corrosion the entire dashboard and climate box has to come out, not a do it yourself job.

all this 3 problems interrupt the operation of the immobilizer and set the blinking light and code b2799. the only thing you can do is inspect the fuse box connect end disconnect al the connectors of the box if you see corrosion cleaned with a little brush, if you see broken wires repair them

If you need further help, I’m available over the phone at https://www.6ya.com/expert/flavio_517b938f50183b92

the audio interrupt wire does not need to be hooked up for the output to work. make sure you have no bad speakers or shorts in the speaker wires. you may want to make sure the interrupt wire isn't shorted to anything also.

E024 The developing assembly connector is disconnected/Disconnection of Toner sensor.
0000 The connection detection signal is absent
continuously for 100 msec. Replace the developing assembly toner sensor. Connect the connector. Replace the DC controller
PCB.
0001 Disconnection of the wire used for detecting the
connection of the toner level sensor is found.
When the disconnection of the wire used for
detecting the connection of the toner level sensor
has been detected for 7.5 min without
interruption (12.5 min in the manual /envelop
cassette feeding).
When the disconnection of the wire used for
detecting the connection of the toner level sensor
has been detected for 12.5 min without
interruption.
-iR4570/3570/3530
When the disconnection of the wire used for
detecting the connection of the toner level sensor
has been detected for 7.5 min without
interruption (12.5 min in the manual /envelop
cassette feeding).
-iR2870/2270/2230
When the disconnection of the wire used for
detecting the connection of the toner level sensor
has been detected for 12.5 min without
interruption.
Correct the cable. Replace the sensor.


TRY THIS:

Remove toner and check for broken parts on tube, check the connection of toner assy, reconect all connectors on dc controller pcb.

If you removed the toner assy before the error occcured check if all connectors are properly inserted.

if you feel you have the technical ability and tools like standard socket set wire crimpers and crimp terminal you may be able to do it ... the unit is most likely installed under the dashboard by the steering column ... where the wires are .... you'll have to reconnect the wire(s) that were interrupted and disconnect two more and tape up any bare wires it all depends how or what materials the installer used. On the Yukon there will be a wire from the Immobilizer to the Thick Red wire of the Yukon ... and a wire connected to the thick pink wire of the Yukon .... and there will be 2 wires from the Immobilizer to an either thick yellow or thick purple wire that was cut ... remove those two wires from the immobilizer and reattach that wire with a Yellow or blue barrel crimp whichever fits best

Although you probably have found the problem by now (~ month ago) -Some factory alarms can interrupt the ignition path if tripped and not reset within a certain time. It kind of sounds like yours is permanently interrupted.
It might be of use to someone else if you reply with any solution you found so others can benefit from your education on the problem.