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. Use instructions for your exact device and software version. If Windows cannot start, see the startup guide.

Work through these checks

0 of 3 complete
01Measure 12V rail with multimeter at Molex connector
  1. Measure 12V rail with multimeter at Molex connector
What to expect

Check whether the original symptom still occurs.

If it does not help

Continue only if this check applies to your device. Consult its manufacturer if you are unsure.

Browse related errors
02Reduce system power draw temporarily
  1. Reduce system power draw temporarily
What to expect

Check whether the original symptom still occurs.

If it does not help

Continue only if this check applies to your device. Consult its manufacturer if you are unsure.

Browse related errors
03Replace with a higher-quality PSU
  1. Replace with a higher-quality PSU
What to expect

Check whether the original symptom still occurs.

If it does not help

Continue only if this check applies to your device. Consult its manufacturer if you are unsure.

Browse related errors

Possible causes

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