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HomeResourcesModbus GlossaryException 04 — Slave Device Failure
Errors & ExceptionsModbus Term

Exception 04 — Slave Device Failure

The slave encountered an unrecoverable error while processing the request.

Definition

Exception code 04 (Slave Device Failure) means the slave understood the request but failed to execute it due to an internal error — hardware fault, I/O error, or an unrecoverable condition. This is the catch-all exception for server-side failures. If you receive this repeatedly, inspect the device's own diagnostic registers or error logs.

Quick Facts

Code hex0x04
CauseInternal slave error during execution
FixCheck device diagnostics or contact vendor

Related Terms

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ModPackQT Modbus Glossary · Updated 2026