PowerEdge: CPU Machine Check Errors

What Are CPU Machine Check Errors?

On PowerEdge servers that use standard BIOS and iDRAC firmware, machine checks are captured into the system event log (SEL). These entries are also reflected in the Lifecycle Controller log (LCL) under various Enhanced Error Message Initiative (EEMI) event codes.

Log Examples

2026-02-24 05:59:06 45773 CPU4003 A Machine Check event error occurred because the CPU received invalid data (DCU, 0xFB80000000110134).
2026-02-24 05:59:01 45764 CPU0704 CPU 2 machine check error detected.
2026-02-24 05:59:01 45763 CPU4003 A Machine Check event error occurred because the CPU received invalid data (DCU, 0xFB80000000110134).
2026-02-24 05:58:56 45754 CPU0704 CPU 1 machine check error detected.
2026-02-24 05:58:44 45741 CPU0704 CPU 2 machine check error detected.

2022-10-22 22:12:35 506 CPU9000 An OEM diagnostic event occurred.
2022-10-22 22:12:34 505 CPU9000 An OEM diagnostic event occurred.
2022-10-22 22:12:33 504 CPU9000 An OEM diagnostic event occurred.
2022-10-22 22:12:31 503 CPU0704 CPU 2 machine check error detected.
2022-10-22 22:12:31 502 UEFI0078 One or more Machine Check errors occurred in the previous boot.

2025-05-21 03:42:32 320 CPU9000 An OEM diagnostic event occurred.
2025-05-21 03:42:30 319 CPU0704 CPU 1 machine check error detected.
2025-05-21 03:42:29 318 PST0090 A problem was detected related to the previous server boot.
2025-05-21 03:42:29 317 UEFI0078 One or more Machine Check errors occurred in the previous boot.

2021-09-02 16:02:18 712 UEFI0078 One or more Machine Check errors occurred in the previous boot.
2021-09-02 16:02:18 711 CPU0000 Internal error has occurred check for additional logs.

2026-02-17 22:12:12 16725 CPU4001 The Machine Check system address reported by the processor is 0x0000000075A2747B.
2026-02-17 22:12:12 16724 CPU4004 A Machine Check event error occurred because of a timeout while the CPU accessed an external device or component: (MLC, 0xBE00000000800400).
2026-02-17 22:11:59 16715 CPU0704 CPU 1 machine check error detected.
2026-02-17 22:11:56 16713 UEFI0078 One or more Machine Check errors occurred in the previous boot.

Understanding Causes of CPU Machine Check Errors

CPU Machine Check Errors (MCEs) have multiple possible causes, ranging from hardware to software triggers. These errors can be attributed to various factors, including:

• BIOS firmware or CPU microcode
• Motherboard CPLD firmware
• Memory errors
• PCIe fatal bus errors
• OS crash or software and driver faults (BSOD, PSOD, or kernel panics)
• CPU faults

The hardware logs can be used to help identify possible causes by checking if other component errors accompany the CPU Machine Check Errors.

Example CPU MCEs triggered from a memory error:

Example CPU MCE triggered from a fatal bus error:

Example CPU MCE triggered from an OS crash:

General Guidance

It is always helpful to ask these questions:

• Have there been recent changes to the system, like updates or changes to hardware or configuration?
• Are there other errors in the logs nearby that may be more informative than the machine check itself?
• How frequently does the machine check happen? Was it a one-off? Can it be readily reproduced?
• Are there environmental factors involved, such as specific workloads or power and thermal scenarios?

Firmware and Drivers

Outdated or incompatible firmware and drivers are among the most common machine check culprits, as they work together to implement and control device behavior. It is essential to update firmware as part of assessing or resolving any machine check errors.

Among firmware, BIOS updates are critical:

• Most BIOS releases incorporate updates provided by the respective processor vendor, many of which include explicit fixes for machine checks.
• These UEFI updates for servers include microcode, reference code, and other module updates that control functionality including all reliability, availability, and serviceability (RAS) features among others.
• Simultaneously, do not overlook other firmware in the system.
• Virtually any device in the system may be the culprit, including on rare occasion the iDRAC.

Identifying and Resolving CPU Machine Check Errors

To identify CPU Machine Check Errors, start by checking the hardware logs Lifecycle (LC) or System Event Log (SEL) from the iDRAC directly, or gather a TSR or SupportAssist Collection to review the logs.

• PowerEdge: Export a SupportAssist Collection Using an iDRAC
• PowerEdge: How to View or Clear the System Event Log
• iDRAC9 User's Guide - Viewing Lifecycle Log from the Web Interface

Look to see if the CPU MCE errors are preceded by any other errors, and if they are, focus troubleshooting on those components.

Troubleshooting Steps

• Update all available firmware and monitor the results for any changes in error behavior.
• If the MCE is triggered from another component's error, focus the troubleshooting on that component.
  • Check what components are controlled by the CPU with the MCE.
  • For example: If it is a CPU1 MCE, check all risers and PCIe slots that are controlled by CPU1 and any devices installed in those slots, as well as memory on the CPU1 side. Check all A-DIMMs for errors.
  • To verify which CPU controls each riser or slot, see the server's Installation and Service Manual and look under Installing and removing system components > Expansion cards and expansion card risers > Expansion card installation guidelines.
  • For more information about identifying which CPU controls the risers or slots, see: PowerEdge: Troubleshooting PCIe device detection issues
• To rule out OS-related MCE triggers, test outside of the OS to see if the errors are still triggered.
  • Run ePSA diagnostics to see if any errors are triggered during the tests.
    • PowerEdge: How to Run Hardware Diagnostics on your Server
  • Boot the Support Live Image (SLI) media to test if errors are generated in that OS environment.
    • PowerEdge: Running Stress Tests in SLI Support Live Image

  Run Stress Tests in Support Live Image

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CPU4002 through CPU4004

These three are diagnostically equivalent; they all highlight a machine check that is unlikely to be the processor and steer focus elsewhere.

• CPU4002: A processor machine check event occurred because the CPU detected an error in an external device (<component_name>, <register reading>).
• CPU4003: A machine check event error occurred because the CPU received invalid data (<component_name>, <register reading>).
• CPU4004: A Machine Check event error occurred because of a timeout while the CPU accessed an external device or component: (<component_name>, <register reading>).

CPU4005

CPU4005: A machine check error was reported by the CPU: (<component_name>, <register reading>).

This message is logged for machine checks that are more likely to be a true processor failure than most machine checks are.

However, it is still important to follow the Recommended Response Action that is included with CPU4005 of updating the BIOS. Microcode updates, which are included with PowerEdge BIOS releases, sometimes include fixes for this class of machine check.

Machine checks that result in a CPU4005 event do not also log a CPU4001 event.

CPU4001

CPU4001: The machine check system address reported by the processor is <registerReading>.

The Recommended Response Action for CPU4001 suggests mapping the address register to a system device. See Resolving machine checks on PowerEdge & leveraging platforms - CPU0011, CPU0012, CPU0704, UEFI0076, UEFI0078 for two approaches to mapping PCIe devices.