AHT Error 4VDC/3/40000003:video controller

I got the same error with a similarly updated 2009 Mac Pro. It's unlikely to be problem, as per https://forums.macrumors.com/threads/apple-hardware-test-error-4vdc-1-40000003-v ideocontroller.1978486/

See post #5: "I ended up downgrading the firmware back to 4,1 from 5,1 and AHT now shows no errors."

More info here:

https://www.macintouch.com/readerreports/macpro/topic4356-003.html

See Oct. 1 post in which:

And "4VDC/3/40000003 : VideoController" did not go away ... until I discovered that I'd only put the AHT for (5,1) on one of my disks, and AHT for (4,1) was still on the other two. So after copying (5,1) AHT to those other two locations (version 3.31-3A207 by the way), AHT finally let me off the hook, reporting no errors. And everything seems to be working fine, for the time being.

He seems to be saying you should run the 2010 version of AHT, although that doesn't entirely make sense to me, since the hardware is still 2009.

You guessed it. The video is definitely at issue here. Bring it in for service to an authorized center to get isolated where the issue is.

If your graphics card is after market, I would try to replace that and see if getting one that is recommended by http://www.xlr8yourmac.com/ helps.

Downgrading and not showing errors does not mean they don't exist. Video RAM and RAM in general is a testing positive can be believed, but testing negative can be doubtful.

The reason has to do with the amount of chips to be tested. Being randomly accessed on off switches, any sequence of switches may be on or off. At 128 Mbit you have 128 million factorial possibilities. Most calculators only give you up to 61 factorial. In other words the number of nanoseconds it would take to test every single combination of circuits that could cause a problem would exceed the age of the Big Bang. 128 Mbit is the same as 128/8 MB.

So even the lowliest graphics chip is more complicated to test than can be done in a human lifetime. If an error is found, it may not be found again, but it is still there.