With Generic Scan Tool

CAN-Bus terminal resistance, checking

Special tools, testers and auxiliary items required
- Multimeter
- Wiring diagram

Test requirement
- A CAN-Bus malfunction was recognized.
- The Engine Control Module (ECM) J220 fuses OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, shift selector lever into position "P" or "N".
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Function
The Engine Control Module (ECM) J220 communicates with other CAN-Bus capable control modules.

The control modules are connected by two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages). Missing information on the CAN-bus is recognized as a malfunction by the Engine Control Module (ECM) J220 and the other control modules connected to the CAN-bus.

Trouble-free operation of the CAN-Bus requires that it have a terminal resistance. This central terminal resistance is located in the Engine Control Module (ECM) J220.

Procedure

- Disconnect the Data Bus On Board Diagnostic Interface J533 electrical harness connector.

Note: The Engine Control Module (ECM) J220 must remain connected for the following step.

- Using a Multimeter, check the Data Bus On Board Diagnostic Interface J533 electrical harness connector terminals 6 to 16 for resistance.

Specified value: 60 to 72 Ohms (at approx. 20�C)

If the specified value was not obtained:

- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).

- Check the wiring connection for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

- Replace the Engine Control Module (ECM) J220.

If the specified value was obtained:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

- Install the Test Box 80 Pin VAG1598/22. Connecting VAG 1598/22 Test Box

If the manufacturers test box is not being used. Perform the following step.

- Remove the Engine Control Module (ECM) J220.

- Using a Multimeter , check the Data Bus On Board Diagnostic Interface J533 electrical harness connector to the Engine Control Module (ECM) J220 electrical harness connector for resistance.




(Engine Code AHA)

Specified value: 1.5 Ohms Max.

If the specified value was not obtained:

- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).

- Check the wiring connection for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

- Replace the Data Bus On Board Diagnostic Interface J533.

Final procedures

After repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code. Audi Drive Cycle/Readiness Code

End of diagnosis.