General Information

GOVERNMENT REQUIREMENTS
^ Standardized Data Link Connector (DLC) located in the vicinity of the driver.
^ Standardized Diagnostic Trouble Codes (DTC) for all manufacturers.
^ Display of emission-relevant DTC's with commercially available "Generic" Scan Tool.
^ Display of operating conditions under which a malfunction occurs.
^ Definition of when and how emission-relevant errors must be displayed.
^ Standardized designations and acronyms used to identify components and systems.

DESCRIPTION
^ On Board Diagnostics II (OBD II) offers a number of troubleshooting possibilities for checking the vehicle.
^ Most causes of driveability problems can be diagnosed by evaluating information supplied to the Engine Control Module (ECM).
^ Malfunctions that occur while driving and that are recognizable by the system are stored and kept in Diagnostic Trouble Code (DTC) memory.
^ Address Word 01 of the OBD II system can only be used with the VAG 1551 or VAG 1552 Scan Tool (ST).
^ Generic Scan Tool (ST) access of Address Word 33 is possible.

SYSTEM OVERVIEW
^ Only with the use of the VAG 1551 ST are all of the OBD capabilities accessible.
^ The "Rapid data transfer" operating mode of the VAG 1551 scan tool is described in Diagnosis With Scan Tool.
^ Check DTC Memory, function 02, should be carried out with the engine running if possible.
^ Output Diagnostic Test Mode (DTM), function 03, can only be carried out with the engine not running and the ignition switched ON.

MALFUNCTION RECOGNITION
^ When a system malfunction occurs, the Malfunction Indicator Lamp (MIL) may not be switched ON immediately. Rather, the MIL may only light up when a malfunction occurs after two drives, one after another with a prior cold start of -10° to 30°C (14° to 86°F) and the malfunction occurring.
^ The MIL is only switched ON for emission related faults.
^ Address word 33 only lists the malfunctions (DTC's) that switch on the MIL.
^ Address word 01, function 02 lists malfunctions (DTC's) that have not been validated, which the MIL has not yet switched on or will never switch on.
^ Each time the ignition is switched on, the MIL must light up and then go out after the engine starts.
^ If the Engine Control Module (ECM) is disconnected, the voltage supply is interrupted and DTC memory will be erased.