General Information

The control module of a system with OBD detects malfunctions during vehicle operation and stores them as Diagnostic Trouble Codes (DTC's) in a permanent memory. The DTC's remain intact in the memory if the power supply from the battery is interrupted.

The OBD function relates to the electrical and electronic parts of a system; in other words it only registers malfunctions which have an effect on the electric signals.

On Board Diagnostic (OBD) helps technicians perform a more targeted diagnostic troubleshooting. Use the VAG1551/1552 Scan Tools (ST) or the VAS5051 tester to achieve the potential offered by On Board Diagnostic (OBD). To do this, the scan tool and the respective control module must exchange data. They must communicate with each other.

The Data Link Connector (DLC) is the interface for communication between the control module and the scan tool.

Troubleshooting is started by connecting the scan tool to the Data Link Connector (DLC). This establishes a data link between the control module and the affected system.

When the data link has been established, you can then select the required troubleshooting functions provided. The functions represent program sequences within On Board Diagnostic (OBD). After first checking the control module version, start the troubleshooting procedure with "Check DTC Memory" function 02.

Any DTC's which may be stored in DTC memory will be indicated on the display of the scan tool. Diagnostic information leads via DTC tables to possible causes and specific repair procedures.

The OBD distinguishes between "static" and "sporadic" malfunctions. If a malfunction which has been stored as "static" is no longer present when the ignition is switched on, it is converted to "sporadic".

Sporadically occurring malfunctions are indicated as such. "/SP" will appear at right on the tester display.

A sporadic malfunction is erased automatically if it no longer occurs after a certain number of driving cycles.

Static malfunctions remain stored until DTC memory is erased using the Scan Tool (ST).

Check control module version before replacing control module. This appears in the display of the scan tool together with the coding when communication is established between the control module and the scan tool.