Interrupts, error messages, diagnostics and system alarms
4.1 Status and error display of the CPU
CPU 1511T-1 PN (6ES7511-1TK01-0AB0)
30 Manual, 09/2016, A5E36270833-AA
Meaning of the RUN/STOP, ERROR and MAINT LEDs
The CPU 1511T-1 PN has three LEDs to signal the current operating status and diagnostics
status. The following table shows the meaning of the various combinations of colors for the
RUN/STOP, ERROR and MAINT LEDs.
Table 4- 1 Meaning of the LEDs
Missing or insufficient power supply on the CPU.
LED off
LED off
An error has occurred.
CPU is in RUN mode.
LED lit green
LED off
A diagnostics event is pending.
LED lit green
LED off
LED lit yellow
Maintenance demanded for the plant.
The affected hardware must be checked/replaced
within a short period of time.
LED lit green
LED off
LED flashes yellow
Maintenance required for the plant.
The affected hardware must be checked/replaced
within a foreseeable period of time.
Bad configuration
LED lit yellow
LED off
Firmware update successfully completed.
CPU is in STOP mode.
LED lit yellow
LED flashes red
LED flashes yellow
The program on the SIMATIC memory card is
LED flashes yellow
LED off
LED off
CPU is performing internal activities during STOP,
e.g. startup after STOP.
Download of the user program from the SIMATIC
LED off
LED off
Startup (transition from RUN → STOP)
LED flashes
LED flashes red
LED flashes yellow
Test of LEDs during startup, inserting a module.