On Board Diagnostic (OBD), General Information

On Board Diagnostic (OBD), general information

The control module of a system with OBD detects malfunctions during vehicle operation and stores them as Diagnostic Trouble Codes (DTCs) in a permanent memory. The DTCs 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 focused diagnostic troubleshooting. On Board Diagnostic (OBD) functions can be used via operating mode 1 "Rapid Data Transfer" within the VAS5051 tester, VAG1551 Scan Tool (ST) or the VAG1552 mobile scan tool. To do this, the scan tool and the respective control module must exchange data. They must communicate.

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 DTCs 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 VAG1551 scan tool display.

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

Static malfunctions remain stored in DTC memory until the memory is erased using the VAG1551 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.

Additional information for All Wheel Drive (AWD) vehicles with Haldex coupling
The longitudinal acceleration sensor -G251- must be switched off before checking brake system on a dynamometer, initiating basic setting, display group number 040.

Switch ignition off and on again one time to re-activate the longitudinal acceleration sensor -G251-.

All Wheel Drive (AWD) vehicles with Haldex coupling are equipped with "Electronic Differential Lock" (EDL).