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Angela MunozJul 28, 2025
Why is the ERROR light on my Siemens Simatic S7 CPU red?
- DDaniel GordonJul 28, 2025
If the ERROR light on your Siemens Controller CPU is red, it could be due to electrical noise. Ensure the control panel has a good ground connection and that high voltage wiring isn't run alongside low voltage wiring. Also, connect the M terminal on the 24 V DC Sensor Power Supply to ground. Alternatively, the issue might stem from component damage, in which case you should send the hardware in for repair or replacement.