ABB · ACS580Fault Code 5090Critical
ABB ACS580 — 5090 STO Hardware Failure
A safety fault raised when the Safe Torque Off (STO) circuit detects a mismatch between its two channels or a hardware failure.
Updated: 2026-07-05
Symptoms
- Drive refuses to run, shows 5090
- Fault may persist even with STO inputs jumpered
- Mismatch with the safety relay/PLC
Probable Causes
- Timing/mismatch between STO channels (IN1/IN2)
- Break or looseness in STO wiring
- Safety supply (24V) issue
- STO input circuit (opto) failure
Checkpoints
- Measure 24V presence on both STO inputs
- Verify both channels switch simultaneously
- Check STO wiring and terminal tightness
- Verify the safety 24V supply
Solution
Safety functionSTO is a safety function; jumpering/bypass must only be done by authorized personnel for temporary testing. Permanent bypass is prohibited.
If wiring and supply are healthy, the STO input circuit is inspected at board level. See the STO article.
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