Computers and Control Systems: Description and Operation

On Board Diagnostic System Features

The Engine Control Module (ECM) for the Diesel direct injection system is equipped with a Diagnostic Trouble Code (DTC) memory.

If malfunctions occur in the monitored sensors and components, they will be stored in DTC memory together with an indication of the type of malfunction.

Malfunctions which only occur sporadically will have the addendum "sporadic malfunction" on the print out. This type of malfunction will be indicated on the display by "/SP". Sporadic malfunctions can be caused by e.g. a loose terminal or a briefly open circuit. Sporadic malfunctions that do not occur again within 40 warm-up cycles will be erased from DTC memory.

A warm-up cycle is defined as each engine start where the Engine Coolant Temperature is below 49 °C and the engine runs continuously until the temperature reaches at least 71 °C.







The Malfunction Indicator Lamp (MIL) -1- will light up when the ECM recognizes one of the specific DTCs that affects exhaust emissions.

If malfunctions are recognized that affect driveability; the Glow plug indicator light -2- will blink.

Stored malfunctions can be displayed using either the VAG 1551 or VAG 1552 Scantool.The VAG 1552 Scan Tool; however, is not equipped with a printer.

DTC memory must be erased once malfunctions have been eliminated.

After erasing DTC memory, set the Readiness code.