Description of On-Board Diagnostics
System OverviewECM number 8AO 906 266 B (MMS 300)
^ Only with the use of the VAG 1551 Scan Tool (ST) are all of the On Board Diagnostic (OBD) capabilities accessible.
^ The "Rapid data transfer" operating mode of the VAG 1551 scan tool is described in On-Board Diagnostics With Scan Tool VAG 1551.
^ The "Blink Code" output is described in On-Board Diagnostics Without 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.
^ ECM coding capability using the VAG 1551 Scan Tool (ST) "Code Control Module" function 07
^ Adaptive Oxygen Sensor (O2S) control, eliminating the need for the CO Fuel Trim (FT) potentiometer on the Mass Air Flow (MAF) sensor
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 MIL does not light up when the ignition is switched on, bridge the Data Link Connector (DLC) terminals using jumpers from the VW 1594 connector test kit. The MIL must remain lit for as long as the terminals are bridged. If not, or if the MIL does not go out, check DTC memory or use the wiring diagram to determine the cause of the malfunction and repair as necessary.
^ If the Engine Control Module (ECM) is disconnected, the voltage supply is interrupted and DTC memory will be erased.