Diagnostics of the electronic system of automatic air conditioning (A/C) (Mercedes-Benz S-Class W140)

Diagnostic codes can be read from the display of the KV control unit in addition to a special scanner. Malfunction codes are saved even when the battery is disconnected.

Reading codes

1. Turn on the ignition;

2. Move the temperature selection handles to the HI left and LO right positions;

3. Within 20 seconds after moving the handles, simultaneously press and hold the REST and EC buttons for 5 seconds;

4. The LED of the RECIRCULATION key will start flashing and OFF will appear on the display

5. Press the right AUTO button for more than 1 sec. If there are no faults in the memory, E will appear on the left side of the display and FF on the right side. Otherwise, Ebl will be displayed on the left side and the fault code on the right side (refer to the list of KV codes);

6. To display the next fault code, press the AUTO button;

7. To erase the codes after they have been fully read, press the right and left AUTO buttons for more than 2 seconds. The left side of the display shows d, the right side shows FF;

8. Pressing the right AUTO button restores erased codes (compare with the codes recorded earlier);

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9. After deleting the codes, E is displayed on the left side of the display, and FF on the right side;

10. Set the temperature selection knob to the normal position;

11. Turn off the ignition.