Siemens SIMATIC ET 200SP HA, System Manual

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8.4 Communication error "IO redundancy warning" (maintenance event:
error code 121H)
The maintenance event "IO redundancy warning" (error code 121H) indicates an error in the
communication between I/O modules with IO redundancy.
Possible causes are the following:
● Right I/O module defective
● Left I/O module defective
● Terminal block defective
To rectify the error, proceed in the order described below.
Procedure
1. Replace the right module - if the error remains unchanged:
2. Replace the left module - if the error continues:
3. Replace the terminal block.
Note
Switching behavior
As soon as you pull the left module, the right module takes over process management.
With input modules, the process values fail for the maximum duration of the redundancy
changeover time.
You can find information on the redundancy changeover time in the technical specifications of
the respective I/O module.
Additional information
● Error correction: Replacing I/O modules
You can find information on this in the section"Replacing an I/O module (Page 120)"
● Error correction: Replacing a terminal block
You can find information on this in the section "Replacing a terminal block (Page 125)"
Maintenance
8.4 Communication error "IO redundancy warning" (maintenance event: error code 121H)
ET 200SP HA Distributed I/O system
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System Manual, 08/2019, A5E39261167-AD