Pro-face RHAA040: Illegal response for initial communication command

Pro-face HMI Major Communication

Model: GP4000/SP5000 Series | Code: RHAA040

Applicable Systems
GP4000 Series

Symptoms

  • GP-Pro EX display unit shows error RHAA040: Illegal response for initial communication command.

Possible Causes

  • An error occurred on the device/PLC side.

Troubleshooting Steps

  1. Step 1: Check that communication settings and connected device settings are specified properly.
    Communication restored and error cleared

How to Reset

Repower or reset the display unit after correcting the root cause.

Related Pro-face Fault Codes

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Source: Pro-face GP-Pro EX Maintenance/Troubleshooting Manual, T.7.1 Common Display errors (proface.tech/otasuke official)

Category: HMI

Published: 2026-10-16