LH Control Unit Diagnostic Trouble Code (DTC) Memory Function
WARNING: This page is about a different car, the 1992 Mercedes-Benz 400E. However, it is still accessible from the selected car via links, so may be relevant.
The diagnostic module is equipped with a retained memory that retains diagnostic trouble codes even after vehicle battery is disconnected. With ignition on, data can be transmitted over Controller Area Network (CAN) and received by the diagnostic module. If a malfunction occurs while driving, the LH control unit switches to a fixed operating mode and notifies the diagnostic module. If the same malfunction occurs during 2 consecutive trips, the respective Diagnostic Trouble Code (DTC) is stored in memory after engine is turned off. With engine running, MIL is illuminated until the fault is repaired and DTC is erased from memory.