Weird Fault on MicroLogix 1400

I have a fault on a micrologix 1400 that says" The controller cannot communicate with an expansion i/o module. The exact module cannot be determined"

If it doesn't know which module how does it know it can't communicate?

Anyone seen this before?

It probably knows a module is there but cannot get it's details. or it is expecting a module as per the settings for the I/O but as it cannot talk to it, it does not know if the module is faulty or wrong type. there could be a number of possibilities like bus connection poor, module faulty or backplane faulty. (depends on the PLC backplane can effectively be a rack or interconnecting plugs & sockets if the modules are used where they are daisy chained rather than onto a rack.

Hi,
I have seen a fault similar with a Micro 1400 whereby the fault message indicated that there was a fault with an expansion I/O module.
When we replaced the expansion I/O module, the fault remained, so we had to replace the Micro 1400 controller.


Best to have spare parts available for both the controller and the expansion I/O