Power supply · high

How to fixPSU-RAIL-UNDERVOLTAGE

PSU 12V rail undervoltage

What this error means

PSU-RAIL-UNDERVOLTAGE shows up as a high-severity power supply unit (PSU) fault. The PSU's 12V rail is delivering voltage significantly below the ATX standard of 12V ±5% (11.4V minimum). The 12V rail powers the CPU via EPS connectors and the GPU via PCIe connectors. Undervoltage causes instability, unexpected shutdowns, and can corrupt data on storage drives due to incomplete write operations. This usually traces back to PSU degradation over time and PSU operating in high ambient temperature. Use the steps below to track down and fix the cause.

Before you begin

Save open work and back up important files. Note any recent driver or hardware changes. If Windows cannot start, use the startup guide first.

Work through these checks

0 of 3 complete
01Measure 12V rail with multimeter at Molex connector

Measure 12V rail with multimeter at Molex connector.

Use the instructions for your exact device and operating system. Check the manufacturer’s documentation before changing firmware, hardware, or system settings.

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02Reduce system power draw temporarily

Reduce system power draw temporarily.

Use the instructions for your exact device and operating system. Check the manufacturer’s documentation before changing firmware, hardware, or system settings.

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03Replace with a higher-quality PSU

Replace with a higher-quality PSU.

Use the instructions for your exact device and operating system. Check the manufacturer’s documentation before changing firmware, hardware, or system settings.

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Possible causes

  • PSU degradation over time
  • Overloaded 12V rail capacity
  • PSU operating in high ambient temperature