Description of On-Board Diagnostics

On Board Diagnostic (OBD) II Technical Data

Memory
- Permanent memory (If the engine control module is disconnected from the permanent battery positive voltage (B+) supply, the Diagnostic Trouble Code (DTC) memory and "Readiness Code" will be erased.)

Data output
- Rapid data transfer
- Additional malfunction display by Malfunction Indicator Light (MIL) lighting up

Address Words:

Functions Under Address Word 01:

Modes Under Address Word 33:

- Under address word 33, Mode 1 to Mode 5 can be selected starting from control module 8D0 906 266 and Mode 1 to Mode 7 starting from control module 8D0 906 266 A.
- Individual measuring values can be read under Mode 1. This is not recommended for Audi service department since this information is available more easily under address word 01, function 04 and/or function 08.
- Mode 2 shows the operating conditions under which a malfunction was recognized.
- Mode 3 is used to check the DTC memory and Mode 4 is used to erase the DTC memory. In the Audi service department, only address word 01, function 05 should be used to erase, since with Mode 4 the DTC memory is erased immediately even if it was not checked first.
- Static variables of HO2S probes, required by legal regulations, are displayed under Mode 5. Since these variables have no direct relationship to HO2S diagnosis, Mode 5 is not needed by the Audi service department.
- Mode 6 is used to read all test results from components and systems that are NOT continuously monitored.
- Mode 7 is used to read test results of components and systems that are continuously monitored.

Malfunction Indicator Lamp (MIL), Functions







- The Malfunction Indicator Lamp (MIL) must light up every time the ignition is switched on and go out after the engine starts. If a malfunction is recognized by the engine control module or the transmission control module, this is indicated by the MIL lighting up.
- If the MIL lights up continuously, there is a malfunction present that makes the exhaust gas worse. In this case, the DTC memory for the engine control module and/or the transmission control module should be checked.
- If the MIL starts to blink, there is a malfunction that can lead to damage of the three way catalytic converter (e.g. combustion misfiring with high misfiring rate). In this case, driving should only continue with reduced power (until the MIL goes off or lights up continuously) and the malfunction should be eliminated as quickly as possible.

Functional testing:
- Switch ignition on: the MIL must light up. If the MIL does not light up, check wiring according to wiring diagram and/or replace lamp.
- Start engine and let idle: MIL must go out after a couple seconds. If the MIL does not go out after the engine starts, check DTC memory for the engine and/or transmission control modules (malfunctions in DTC memory).

Malfunction recognition and repair
- Before initiating the On Board Diagnostic (OBD) program, and before testing wiring and replacing components, check the following ground connections for corrosion and damaged connections and repair them if necessary

- Check ground connections on intake manifold
- Battery ground stap OK
- ground cable between engine and body OK


NOTE:
- Malfunction recognition and repair is described for the VAG 1551 scan tool, since it offers significantly more functions. However malfunction recognition and repair is also possible with a "generic" scan tool.
- A specific procedure must be used to evaluate malfunctions, since the engine electronics can be checked with address word 01 and address word 33 on OBD II vehicles. Address word 33 can only be used to check malfunctions that have already switched on the Malfunction Indicator Light (MIL). Address word 01 can also display the malfunctions that have not switched on the MIL. In contrast to before, the MIL is not switched on immediately with some malfunction types, but only after two successive trips with cold starts preceding them where the malfunction occurs. If there is a customer complaint and/or driving performance problem, the DTC memory should be checked thoroughly with address word 01, function 02. On vehicles with MIL lit up, the DTC memory should also be checked with address word 33, mode 3. If the DTC memory is checked with mode 3, mode 2 should also be checked which shows the operating conditions as they were when the malfunction was recognized.
- If a malfunction is present for longer than a specified time, the malfunction is stored as a static malfunction. Malfunctions that never or immediately switch the MIL on are set as "sporadic" at each engine start. If the malfunction occurs again, the "sporadic" status is erased again. The "sporadic" status is erased exclusively after an OK diagnosis for malfunctions that only switch the MIL on after two successive trips with prior cold start and malfunction occuring. This process repeats continuously. If the malfunction does not occur again within the next 40 engine starts, this sporadic malfunction is automatically erased.
- The MFI control module differentiates among approx. 150 different malfunctions after evaluating the Information, and stores them until the DTC memory is erased. See Diagnostic Trouble Code (DTC) table.
- If possible, the DTC memory should be checked with engine running.
- If no malfunction is stored in the DTC memory, do not additionally erase DTC memory with function 05 since the readiness code (if it has been set) will be erased.
- The DTC memory should only be erased with function 05 since the DTC memory is erased immediately with mode 4 even if the DTC memory was not checked before that.
- If a malfunction recognized by the On Board Diagnostic (OBD) is eliminated, the following work steps should be carried out after that:


- Erase DTC memory
- Stop engine (switch ignition off) and start it again
- Take a test drive
- Carry out automatic test sequence by inserting address word 00


NOTE: Every time the DTC memory is erased (both with function 05 and with mode 4), the readiness code is reset.