F-DO Test Stop Fault (CU)

What does F01773 mean?

A fault has occurred during the test stop procedure on the Control Unit (CU) side, specifically related to the evaluation of states for Fail-safe Digital Outputs (F-DOs). This indicates that the expected states of the DOs or diagnostic DOs were not fulfilled, or an internal timer/state issue occurred, often a mismatch between expected and read-back signals during a test state.

• Failure of a specific Fail-safe Digital Output (F-DO) on the Control Unit (CU) to switch to its expected state during the test stop.
• External wiring fault (e.g., short circuit, open circuit, incorrect load resistance) connected to the F-DO on the CU.
• Incorrect parameterization of the F-DO test stop function (e.g., P9620 "F-DO test stop command", P9621 "F-DO test stop delay") on the CU.
• External component (e.g., safety contactor, valve) connected to the F-DO not responding within the expected time window during the test.
• Internal hardware defect of the F-DO channel or its associated test circuitry on the Control Unit.

Click steps to track your progress.

1. 1

   1. Identify the specific F-DO (e.g., F-DO1, F-DO2) that failed the test by reviewing internal safety diagnostics (r9625).

2. 2

   2. Measure the voltage at the output terminals of the problematic F-DO (e.g., X126/1, X126/2) on the CU during a test stop sequence.

3. 3

   3. Disconnect the external load from the problematic F-DO and re-run the test stop procedure to isolate internal vs. external fault.

4. 4

   4. Verify the wiring continuity and insulation resistance (using a megohmmeter) of the cable connected to the F-DO.

5. 5

   5. Review parameter settings for F-DO test stop (e.g., P9620, P9621) and ensure they align with the safety application requirements.

6. 6

   6. If the fault persists with no external load, consider replacing the Control Unit after thorough diagnostics.