What causes Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault Slave not in OP?

1. Stuck in INIT: device not reached or identity does not match: Run an online scan and compare vendor, product code and revision; check cabling and supply to the device. 2. Stuck in PREOP: process data or DC configuration refused: Read the AL status code in the logger and fix the configuration it names. 3. Stuck in SAFEOP: no valid outputs, sync or watchdog problem: Check that the task writing the outputs runs, and the DC/sync diagnosis.

EtherCAT Slave Stuck in INIT, PREOP or SAFEOP: Causes

In normal operation every slave is in OP (State = 8). Each state shows how far startup got: INIT – no mailbox or process data yet; PREOP – mailbox works, the master is writing SyncManager, FMMU and PDO settings; SAFEOP – SyncManagers and DC were accepted, inputs update but outputs are held in a safe state; OP – the master must transfer valid outputs before SAFEOP→OP. A slave that stops at one state usually reports why with an AL status code.

Diagnose this with AI

Upload a keypad photo, the fault history or a parameter export from your Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT. InduQT compares the evidence and suggests the next useful checks.

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When it happens

At EtherCAT startup after activating a configuration or restarting TwinCAT
In operation, when a slave drops back from OP

Likely causes and checks

1Stuck in INIT: device not reached or identity does not match

Points to it: State 0x0101 (INIT + not present) or 0x0020 (invalid vendorId, productCode); RUN LED off.
Check: Run an online scan and compare vendor, product code and revision; check cabling and supply to the device.

2Stuck in PREOP: process data or DC configuration refused

Points to it: AL status such as 0x0024/0x0025 (mapping) or 0x0030 (DC); RUN LED flashing.
Check: Read the AL status code in the logger and fix the configuration it names.

3Stuck in SAFEOP: no valid outputs, sync or watchdog problem

Points to it: AL status 0x001B, 0x001A or 0x0019; RUN LED single flash.
Check: Check that the task writing the outputs runs, and the DC/sync diagnosis.

Telling it apart

Beckhoff warns that "Auto restore states" can deadlock: if the master resets the slave toward OP but only reaches SAFEOP before another fault, it keeps trying SAFEOP only; Beckhoff advises controlling master and slave states from the application.
Restarting a slave from INIT to OP usually disconnects its outputs; make sure the machine is in a safe state before forcing state changes from the online view.

Evidence to collect

EtherCAT online tab screenshot (State of all slaves)
Logger export with AL status codes
Photo of the RUN LEDs
Online scan compared with the configuration

Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.

Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault Slave not in OP: EtherCAT slave stuck in INIT, PREOP or SAFEOP