B2958 Security System

B2948: Security Sensor Signal Circuit Voltage High

This code sets if the BCM detects battery voltage on the sensor circuit (Yellow wire) for more than 1-sec after the ignition switch has been turned off. It is a short to battery power between the sensor supply circuit (white wire) to the sensor circuit (yellow wire).

Does the Security light come on and stay on? If so you need to determine if the location of the short in the wiring, it is likely near the location they removed the alarm module from.
If you have a transponder key that works then it isn't the issue, however if that alarm also had a remote start then there may be a bypass box installed that is causing the problem as they made different ones that are supposed to fool the system into thinking the key is there to allow it to start. They fail and cause problems.

If there is only one working key I would get a second one made. Far to easy to be locked out of modern vehicles. However most locksmiths these days can cut and program keys so you don't really need to take it to a dealer for that.
As for who to take it to that is a tough call as finding a good shop that you can trust is a bit like finding a needle in a haystack. I generally say to talk to the folks you know who have vehicles and ask them and see who they recommend or don't. Word of mouth is a great tool and for bad shops it can put them out of business.

The code is basically saying there is a shorted wire in the security system. The issue then is where is it and why is it. For that you want someone good with electrical diagnostics. That is the difficult part. I have seen guys working out of a van who could diagnose a car electrical problem correctly in less time than it took to read to this point. I have also seen dealerships that have a vehicle for 4-5 weeks and cannot find the problem who then call them in because they don't have the skills needed. It's finding that good shop that is the issue. If your regular mechanic does good mechanical repairs and most others but gets stuck on these codes, I'd say keep them for that. IF you trust and like their work.

As for the key, it depends on the vehicle. Some have 3-4 keys or fobs with each being programmed to allow the car to do different things. Like reduced engine power in the case of a high performance car, or like many luxury cars the key tells the car to adjust the seats, mirrors, pedals, radio stations and more just by reading the transponder in the key. Others are more basic and just tell it, Yes I'm a valid key. Your Vue should be the more basic key. So any valid key in the system works.

It sounds like he is on the correct track. The system has a short in it and reaching out to the dealer was a good call as they have likely seen this fault other times. I have seen the same code in other vehicles but not recently. In my area most Saturn's have returned to the steel and plastic they started from. Let us know what they do and what happens, it might just help another person with their Vue, and please feel free to return with any other automotive questions.