Check Buttons In Operating Unit & Coding Diode
Check buttons in operating unit and coding diode (matrix circuit). ^D^ 205/207/208 Status listsPossible cause:
Pc-board of operating unit, connection to control unit, switch, button or corresponding diode defective
NOTE: The "auto" buttons switch on the function diode only internally. The control unit detects "auto" when no button is depressed. The buttons are detected by the control unit via a contact connected in series with a diode. When the control unit detects a button, this status can be read out in the status lists ^D^ 205/207/208.
Checking the buttons in the operating panel.
Test equipment:
Adapter with correct connection lead (26-pin blue), Service Tester ^M^ 09 Diode test.
Test prerequisite:
Adapter connected to operating unit (blue connector), control unit side not connected, ignition switched off. The pin numbers without brackets ( ) apply when the adapter is connected at the control unit connector and the control unit side is not connected (yellow connector SRB X614).
Button Testing Chart
Notes on Chart
x = Button depressed / independent heating or independent ventilation "ON" / right-hand drive operating unit with coding diode
o = Button not depressed / independent heating or independent ventilation "OFF" / left-hand drive operating unit without coding diode
Notes on Independent heating/ventilation
The switch and diode are integrated in the relay box. With the aid of their output temperature sensor, the on-board computer or the multifunction timer decide whether the independent heating or independent ventilation systems are to be activated. For test purposes, the on-board computer can switch on the independent heating or independent ventilation system in inverse mode.
Notes on evaluation
If the specified displays, referred to the pin numbers in brackets, are not obtained or it short-circuit is indicated, then the pc-board of the operating unit or the corresponding contacts are defective. If the displays are not obtained when checking at the connector X614 (pin numbers not in brackets) the corresponding wires must also be checked in accordance with the schematics.
Test Schematic for IHKA Program Buttons