BECKHOFF KL1904 - Manual (Page 32)

Operation
30 KL1904
4.3.1.3 Diag 3 (red) and Diag 4 (red)
The Diag 3 and Diag 4 LEDs indicate internal terminal errors.
Note
Returning the terminal
These errors lead to shutdown of the terminal. The terminal must be checked by
Beckhoff Automation GmbH & Co. KG.
Diag 3 LED (red) Diag 4 LED (red) Source of error
lit flashes (see below for flashing
codes) µC1
lit off µC2
In the event of a fault the Diag 4 LED indicates the type of error through flashing codes. The flashing
codes are structured as follows:
Flashing sequence Meaning
Rapid flickering Start of flashing code
First slow sequence Error code
Second slow sequence Error code argument
Start Error code Error code argument
Count the number of flash pulses after the rapid flickering sequence
 during the first slow sequence in order to ascertain the error code
 during the second slow sequence in order to ascertain the error argument
The flashing code is repeated after the second slow sequence, followed by rapid flickering.