On Board Diagnostic Technical Data
MEMORY:^ Permanent Memory
^ If power (B+) is disconnected from the Engine Control Module (ECM), the Diagnostic Trouble Code (DTC) memory as well as the "Readiness Code" are erased.
DATA OUTPUT:
^ Rapid data transfer, Address Word 01
^ Rapid data transfer, Address Word 33
^ System malfunction is also indicated by the Malfunction Indicator Lamp (MIL) staying ON.
AVAILABLE FUNCTIONS OF ADDRESS WORD 01:
^ Function 01: Check Control Module Versions
^ Function 02: Check DTC Memory
^ Function 03: Output Diagnostic Test Mode
^ Function 04: Basic Setting
^ Function 05: Erase DTC memory
^ Function 06: End Output
^ Function 08: Read Measuring Value Block
AVAILABLE MODES OF ADDRESS WORD 33:
^ Mode 1: Transfer diagnostic data
^ Mode 2: Operating conditions
^ Mode 3: Check DTC memory
^ Mode 4: Erase diagnostic information
^ Mode 5: Heated Oxygen Sensor - probe output signals
NOTES:
- Use VAG 1551 Scan Tool (ST) to access all functions of the OBD II On Board Diagnostic system.
- Only Address Word 33 functions are accessable with a Generic Scan Tool.
- Access DTC memory with engine running.
- The ECM can identify approximately 110 different malfunctions.
- Malfunctions are stored as Diagnostic Trouble Codes (DTC's) in the DTC memory.
- DTC's remain stored until a specific number of cold starts and drives without the malfunction reoccurring (at which time the DTC will be erased) or the memory is erased using a Scan Tool.
- With OBD II, the Malfunction Indicator Lamp (MIL) is not immediately switched ON for some malfunctions. Rather, the MIL may only light up when a malfunction occurs after two drives, one after another with a preceding cold start of -10° to 30°C (14° to 86°F).
- Malfunctions in which the MIL does not immediately switch on are set to "sporadic" at every engine start. If the malfunction occurs again, after two drives, one after another, then the MIL will light up and the malfunction will no longer be sporadic.
- Malfunctions in which MIL comes on can only be read and erased using the VAG 1551 Scan Tool or a generic Scan Tool.
- Perform Output Diagnostic Test Mode (DTM), Address Word 01, Function 03, with ignition switched ON, engine OFF.
- Each time the ignition is switched ON, the MIL lights up then switches OFF after engine is started.
- If the MIL does not light up when the ignition is switched ON, check the bulb (replace if necessary), then check wiring according to the wiring diagram.
- If the MIL does not go out after starting the engine, or lights up while driving, check DTC memory.
- If the MIL starts to flash while driving, combustion misfire with high misfire rate has been identified. If this occurs, drive only at a reduced speed and do not subject the engine to heavy loads (i.e. rapid acceleration). Check DTC memory and repair malfunction as soon as possible, since the Three Way Catalytic Converter (TWC) could be damaged. If the MIL stops flashing, normal engine operation can be resumed.
- If a driveability problem or customer complaint exists and the MIL has not been switched ON, check DTC memory using address word 01, function 02 (this will identify a malfunction that may not switch on the MIL immediately).
- If the MIL is ON, check DTC memory using address word 01, function 02 or address word 33, mode 3. Address word 33, mode 3 only indicates DTC's that have switched ON the MIL.
- If the DTC memory is checked using address word 33, mode 3, also check mode 2, which indicates operating conditions at the moment the malfunction occurred.
- Erase DTC memory using address word 01, function 05 or address word 33, mode 4. It is recommended that only address word 01, function 05 be used to erase the DTC memory because address word 33, mode 4 immediately erases the DTC memory, even if the memory has not previously been checked. Useful diagnostic data may be lost if the DTC memory is erased without checking the the DTC memory.
- Disconnecting the ECM harness connector interrupts power supply (B+) to the ECM and will erase the DTC memory as well as the "Readiness Code."
- After repairing a malfunction (DTC), carry out the following work procedure:
^ Erase DTC memory using VAG 1551 Scan Tool, address word 01, function 05.
^ Stop engine (switch ignition OFF) then restart.
^ Test drive vehicle (leave VAG 1551 ST connected).
^ Initiate "Automatic test sequence" by entering address word 00. The automatic test sequence will check all systems with OBD and print out any malfunctions (DTC's).