1 PCM connector
2 Microprocessor
3 Operating memory (RAM)
4 EEPROM memory
5 PATS
6 Power supply relay
7 Fuse
8 Battery
NOTE: DTCs and adaptation data can be deleted electronically with the aid of WDS.
NOTE: The PCM has a continuous voltage connection to the battery. This is used, among other things, to activate the PATS LED.
To store DTCs and other data, the PCM uses the EEPROM memory on diesel engines.
The EEPROM memory is a non-volatile memory (read-only memory) which means that the data contained in it are retained even if the supply voltage is interrupted (e.g. when the battery is disconnected).
During a journey, all new fault codes and engine adaptation data (e.g. fuel adaptation data) are first stored in the operating data memory (RAM) of the PCM.
After the engine is switched off, and at certain intervals during operation, these data are then transferred to the EEPROM memory. To ensure this happens, the power supply relay remains activated for a further 1.2 seconds after the ignition is switched off (power latch). After the ignition is switched on, the DTCs stored in the EEPROM are transferred back to the RAM memory.
