Information Bus: Testing and Inspection

Diagnostic Procedures

CAN-Bus, Checking Terminal Resistance

The Engine Control Module (ECM) communicates with all databus-capable control modules via a CAN databus.

These databus-capable control modules are connected via two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages). Missing information on the databus is recognized as a malfunction and stored.

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

Special tools, testers and auxiliary items required

• Multimeter (VAG1526) or Multimeter (VAG1715)

• Connector test kit (VAG1594)

• Wiring diagram

Test requirements

• A CAN-bus malfunction was recognized via On Board Diagnostic (OBD) , Diagnostic mode 3: Check DTC memory.

• Ignition switched off.

Test sequence

- Connect test box to Engine Control Module (ECM) , connecting test box for wiring test. During this, wiring harness to Engine Control Module (ECM) is not connected.





- Check central termination resistor in the Engine Control Module (ECM):

- To do this, measure resistance between test box sockets 58 + 60:

Specified value: 120 to 144 ohms

If resistance value is not in specified range:

- Replace Motronic Engine Control Module (ECM) (J220).

If resistance value is in specified range:

- Eliminate malfunction in Data-Bus wires or in other Data-Bus components according to wiring diagram:

Final Procedures

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

1. Check the DTC memory. Refer to --> [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to --> [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to --> [ Readiness Code ] Readiness Code.