IO-Link faults — master/port, IODD, device config

IO-Link is a point-to-point connection between a sensor/actuator and an IO-Link master (not a fieldbus) — increasingly popular for smart diagnostics & parameterization. When a device won't enter IO-Link mode, the port faults, or parameters don't load, the cause is usually port class, cable, IODD or the master config.

Common causes

1. Port not in IO-Link mode — left in SIO, or the master hasn't configured that port.
2. Cable / pins — wrong cable, pin 4 (C/Q) not connected, cable too long.
3. Class A/B mismatch — a device needing auxiliary power (Class B) plugged into a Class A port.
4. IODD — missing the correct IODD for the device + revision.
5. Parameters after replacement — the new device hasn't reloaded parameters (data storage not enabled).

Step-by-step diagnosis

1. Enable IO-Link mode on the port In the master config, set the port to IO-Link (not SIO) for that device.
2. Check cable & pins Use a proper cable, verify pin 4 (C/Q), length ≤20m; try another cable.
3. Match Class A/B A device needing aux power must use a Class B port (or proper supply).
4. Load the IODD Add the correct IODD model + revision into the engineering tool to read/set parameters.
5. Enable Data Storage Let the master auto save/restore parameters → swapping a sensor reloads them automatically.
6. Read diagnostics Check the port event/diagnostic to tell a comms fault from a device fault.

When to call an expert

IO-Link is convenient, but class/IODD/data-storage faults get messy when replacing devices. DeepDebug supports remote master + parameter configuration, including integrating the IO-Link master onto Profinet/EtherNet/IP.