Self-diagnosis function
Each ECU has a self-diagnostic capability in which it continuously monitors signals from certain sensors and engine actuators and compares each signal to a table of programmed values. If the diagnostic software detects a malfunction, the control module stores one or more trouble codes. DTCs will not be stored if there are no codes for individual part faults or for conditions not covered by the diagnostic software. Depending on which control system is installed, the control unit will issue either two-digit or three-digit fault codes, therefore, appropriate fault code readers must be used to read them.
Bosch Motronic 1.2
Early BMW VI2 engines are equipped with the Bosch Motronic 1.2 system with two electronic control units. Each control unit belongs to a group of 6 cylinders (ECU 1 to the right group and ECU 2 to the left group) and collects data from its own sensors. Each electronic control unit remembers its own fault codes and must be serviced independently of the other.
Limited mode
The BMW vehicle systems discussed in this chapter use the emergency mode function. When certain faults are identified (not all faults trigger limited operation mode), then the electronic control unit starts the limited operation mode and will be guided by the programmed values, and not by the signals from the sensor. This allows the car to safely reach the place of diagnosis and / or repair. When the fault is cleared, the control unit will return to normal operation.
Ability to adapt or «learning»
BMW systems also use an adaptive function that modifies basic programmed values for the most efficient operation under normal conditions and to compensate for wear on engine parts.
Control lamp of system of self-diagnostics
BMW models are equipped with a CHECK ENGINE indicator lamp mounted on the instrument panel. Fault codes indicating malfunctions of parts related to the exhaust system can be read using the indicator lamp flashes.
The self-diagnostic plug is for use only with a trouble code reader and is located in the engine compartment on the left or right fender, or near the bulkhead of the engine compartment, or near the suspension strut.