The passlock system cannot be removed; that is one of the features that makes it so effective. The passlock system is built into several components in the vehicle, so no part can be removed without disabling the vehicle.
The body control module is only one component involved in the security system on your Impala. Since replacing teh BCM DID repair the problem for 6 months, it is very likely that they diagnosed and repaired the vehicle correctly at that visit. you could have some other component failing that is giving you the present starting issues.
The most common component that wears out and causes the security sstem to disable the vehicle is the hall effect sensor that is part of the ignition lock cylinder assembly. This component contains all of the mechanical moving parts in the system, and is usually one of the first failure components.
To diagnose and repair the problem, you are going to need to have the vehicle towed in to the GM dealer, or an independent shop equipped with a Vetronix tech-2 scan tool. This is the only piece of equipment that can commonicate with and program the security system on GM vehicles. When the passlock system malfunctions, it stores fault codes and other information just like any other computer system on the vehicle does. A technician with the proper equipment can access this data to see which component is causing the problem in your vehicle.
After the faulty component is diagnosed and replaced, a Tech-2 is also required to re-program the system to accept the new components so the car will start. Simply plugging in new parts will not make teh system operational; it was designed this way on purpose to prevent car thieves from doing just that.
You may want to take the vehicle back into the shop that repaired the security problem several months ago; obviously they have the proper equipment as well as at least one technician trained in diagnosis and repair of this type of fault. Tthere really is nothing you can do to repair this type of failure at home in the driveway....
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