On Board Diagnostic System Overview

SYSTEM OVERVIEW

^ Only with the use of the VAG 1551 Scan Tool (ST) are all of the On Board Diagnostic (OBD) capabilities accessible.

Functions Available:

Read Diagnostic Trouble Code Memory
Erase Diagnostic Trouble Code Memory
End Output
Code Control Unit
Read Measuring Value Block

^ The "Rapid data transfer" operating mode of the VAG 1551 scan tool is described in On-Board Diagnostics With Scan Tool VAG 1551.

^ 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.

^ ECM coding capability using function 07 of the VAG 1551 Scan Tool (ST), "Code Control Module".

MALFUNCTION RECOGNITION

^ A malfunction that is present for a specified time is stored as a static malfunction. If after a specified time the condition no longer exists, it is defined as a sporadic malfunction and identified with an "SP" in the display. The evaluation repeats continuously. If a sporadic malfunction does not reoccur within the next 50 engine starts, it is automatically erased.

^ In the California version, malfunctions that affect the exhaust and emission control are also displayed by illuminating the Malfunction Indicator Lamp (MIL) in the instrument cluster.

^ Each time the ignition is switched on, the MIL must light up and then go out after the engine starts.

^ If the Transmission Control Module (TCM) is disconnected, the voltage supply is interrupted and DTC memory will be erased.