Apple Hardware Test Sensor Error Codes 4SNS...TMA3 etc.

This is more of an answer to a question I have seen posted elsewhere on the Apple support boards but has not been replied to. Unfortunately, the threads were closed preventing a reply.

However, with regards to using the Apple Hardware Test, if in fact it does find an issue with your machine, often times it will generate a long code without the ability to figure out what the cause is, forcing someone to have to take their Mac in for repair, when the fix could be relatively simple to do yourself.

Recently, I had been experiencing an issue with my older MacPro 5,1 randomly freezing, or failing to wake from sleep all at random times. Running the Apple Hardware Test threw a code 4SNS/1/C0000008:TMA3--124. By itself, without some kind of identifier key, you're lost to figure out what the code means. However, after some searching, I was able to conclude that the 4SNS prefix denotes a sensor and the last suffix TMA3 indicates what type of sensor and where it is located - (T) thermal sensor on the (M) memory riser in bank (3) three.

Simply replacing the identified DIMM solved the issue even though the memory module still seemed to work. On many of the newer Mac models, Apple certified memory includes thermal sensors. Unfortunately, if the sensor fails it can raise havoc on a system causing instability.