This is the vendor-defined major error code number identifying the broad category of the last non-fatal fault on this card. This numeric code is really only actionable when matched against Cascade's error-code reference table, so an admin's real workflow is to capture this value along with cardDiagNonFatalErrMinor and hand both to vendor support or a lookup table rather than interpret them directly from the MIB. For example, a support ticket reports cardDiagNonFatalErrMajor equal to 14, which the vendor's code table maps to a memory-parity category, guiding the next diagnostic step.