The actual test being done here is not documented by Apple. The error indicates a hardware problem.
Details
The check involves RAM testing. The test itself is called a “Mod3 test”.
The test identifies bad RAM chips.
What to do
You will need to replace the SIMM that is bad once you determine which one it is.
One way to determine which chip is bad is to remove one chip at a time and restart until you find the bad one.
One caution, however. Many of the older Mac models required RAM chips be inserted or removed in pairs. You may not be able to do just one chip at at a time. If yours is one of these models, removing 1 chip will result in a Sad Mac icon - but probably a different error code than the one you just got.