Siemens SIMATIC S7-400 Reference Manual page 92

Digital modules
4.4 Diagnostics for digital modules
Diagnostic message
Wire break
Fuse blown
Sensor supply missing Overload at sensor supply
Load voltage L+ miss‐
ing
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Possible cause of error
Lines interrupted
No external sensor supply
Channel not connected (open)
One or more fuses on the module
has blown and caused this fault.
Short-circuit of sensor supply to M
Power supply L+ to module missing Feed in supply voltage L+.
Fuse in module is defective
Remedy
Connect the cable
Wire sensors with10 to 18 kΩ.
Disable the "Diagnostics – Wire break"
parameter for the channel in STEP 7.
Wire the channel
Remove the overload and replace the
fuse.
Eliminate overload
Eliminate the short-circuit.
Replace the module
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08