The best way to determine if the vertical bar is due to the screen is to boot the Mac into an operating system and take a screenshot.
If the vertical bar still appears in the actual screenshot, then you know it's related to something else (e.g. the GPU, etc). If it's not there, it's a problem with the screen.
Another option you could try is to test the hardware by running Apple Hardware Test over the internet.
To do this, follow these steps:
- Shut down the MacBook Pro
- Restart the MacBook Pro
- Press and hold the option and D keys before the gray startup screen appears.
- After a while, Apple Hardware Test (AHT) will start.
- When prompted, select your language and click the right arrow.
- When the AHT console appears, you can choose to run Basic tests by clicking the Test button. However, I suggest you select the "Perform extended testing" checkbox before you click the Test button.
- Your test results will appear in the window in the bottom-right of the console.