For Data Link Connector

Troubleshooting communications faults between VAG1551 Scan Tool (ST) and control modules with On Board Diagnosis (OBD) capability

Requirements:
- Power supply in order.
- Correct address words of all the control modules with OBD capability fitted to car are known.
- Valid current flow diagrams and workshop manuals of the systems with OBD capability are available.

Test equipment:
- VAG1551 Scan Tool (ST) and diagnostic cable VAG 1551/3
- Adapter cable set VAG 1594
- Test box VAG 1598
- Multimeter Fluke 83 (US1119) or equivalent


NOTE: It is not possible to separate the individual K wires of the control modules. When conducting troubleshooting, it is therefore necessary to unplug the individual control module connectors.


1. Engine control module dose not answer


NOTE: If one of the four fault messages below appears in the display of VAG 1551 after selecting engine electronics (address word 01) proceed as follows:

Troubling Shooting Program For Data Link Connector (Part 1 Of 3):

Test step 1.1
- Test diagnostic cable VAG1551/3, and replace if necessary.
- Select engine control module (address word 01) with VAG 1551.
- If the engine control module does not answer, perform next test step.

Test step 1.2
- With the exception of the engine control module, unplug all control module connectors of the control modules fitted to the car.
- Select engine control module (address word 01).
- If the engine control module does not answer, continue with test step 1.3.
- If the engine control module now answers, the fault is at another control module.
- Isolate affected control module by plugging in each module in sequence and resubmitting engine control module address word 01.


NOTE: After rectifying the fault, plug in the connectors again at all the control modules.


Test step 1.3
- Test cable connection and wiring between Data Link Connector (DLC) and engine control module with test box VAG 1598 for open circuit, short circuit to earth and short circuit to positive using wiring diagram.
- If no fault is found in the cable connection, replace engine control module.


NOTE: After rectifying the fault, plug in the connectors again at all the control modules.


2. Control Module dose not answer


NOTE: If one of the four fault messages below appears in the display of VAG1551 after selecting the desired control module or in the case of an 'automatic test run' (address word 00), proceed as follows:

Troubling Shooting Program For Data Link Connector (Part 2 Of 3):

Test step 2.1
- Test diagnostic cable VAG1551/3, and replace it necessary.
- Select the desired control module with VAG 1551.
- If the control module does not answer, perform next test step.

Test step 2.2
- With the exception of the desired control module, unplug all the control module connectors of the control modules fitted to the car.
- Select the control module with VAG1551.
- If the control module now answers, the fault is at another control module. Plug in the connector at the next control module and continue with test step 2.3. Test the engine control module.
- It the control module does not answer, perform the next test step.

Test step 2.3
- Test cable connection and wiring between Data Link Connector (DLC) and connector of the control module with test box VAG 1598 for open circuit, short circuit to earth and short circuit to positive using wiring diagram and rectify it necessary.
- If no fault is found in the cable connection, replace control module.


NOTE: After rectifying the fault, plug in the connectors again at all the control modules.


3. Testing diagnostic cable VAG 1551/3
- Test diagnostic cable for continuity with Multimeter Fluke 83 (US 1119) or equivalent.

Troubling Shooting Program For Data Link Connector (Part 3 Of 3):

NOTE: If no readout appears in the display, the fault may also be a dirty VAG 1551 program card. In this case, clean the contacts of the program card with a lint-free cloth dipped in alcohol and insert the card in to the slot again.