New user here with an 252h fault code. I've tried clearing the fault but it's persistent. Trying to check what should be causing this and how to resolve it.
On SLC-500 controllers, the first two bytes are a Slot number that's causing the fault, so the problem is in Slot 02 (the CPU is Slot 0).
Chapter 16 of the SLC-500 Instruction Set Reference Manual (1747-RM001) shows that Error code 0x**52 indicates that a module that is in the user program is not being detected by the CPU.
A good way to troubleshoot it is to go into the S:11 and S:12 Status bits and disable the Slot. If the fault is then clearable, then it's the module hardware. If the fault moves to another slot number, then it might be the backplane.