hardware test error, 4SNS/1/4000000: IPOR

...what also happens is that the laptop will shut down without warning after i open the laptop, it will start up and then shutdown.

This strongly suggests that one of the temperature sensors is falsely reporting a dangerously high temperature reading, prompting the machine to shut down for its own protection. There is no published information that would enable you to determine which sensor it is, let alone replace or repair it. The only thing to do is have your machine professionally repaired.

My advice is still to take the machine in for service, so a technician who has information about the meanings of AHT's error codes can diagnose the problem.

I'd second the advice from eww, it should be looked at right away.

I've a sneaking suspicion that's actually one of the motion sensors (platform sensor) so you might not be protected in case of a sudden movement and you could get hard drive problems.

A quick google of the code leads to an iFixit forum thread identifying 4SNS as a category of logic board sensor error. IPOR apparently identifies the specific sensor. The recommended troubleshooting / repair advice is:
1. Reboot and see if the problem goes away on its own;
2. Reset the PRAM and NVRAM and see if the problem goes away;
3. Replace the faulty component (or the logic board if required).

As eww indicates, if you are having problems where the computer is shutting itself down you might just want to skip straight to step three...