What this code means

Component / fault: J1939 data.
Reported detail: loss of data signal.
FMI 12 in the SAE J1939 / Caterpillar CDL convention means: Bad intelligent device or component — see the full FMI reference table.

On a Caterpillar display this code may appear as MID/CID 231 with FMI 12, or in the older PID/SID style. Wording of the reported detail follows the public Caterpillar fault-code listing cited below.

First checks (general, for this failure type)

The control module reports an internal or intelligent-device fault. Verify module power and ground first; if they are good, the manual procedure usually ends at module replacement.

These are general electrical checks for FMI 12 faults, not a substitute for the model-specific test procedure. If the fault is active and the machine is derated or shut down, follow the service manual for your model and serial prefix.

Need the part?

If the checks point to a failed sensor, solenoid or harness part, send us the code (231 / FMI 12), the machine model and serial number — we quote genuine and OEM replacement parts for export.

Same component, other failure modes

FMI 2 FMI 11 FMI 14