Information Bus: Testing and Inspection

Data Bus Terminal Resistance, Checking

The ECM communicates with all data bus-capable control modules using a CAN-data bus.

These data bus-capable components 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 resistance is located in the Engine Control Module (ECM).





Special tools, testers and auxiliary items required

• Multimeter (VAG1526) or Multimeter (VAG1715)

• Test adapter kit (VAG1594A)

• Test box (VAG1598/31)

Test Prerequisite

• Ignition switched off.

Test Sequence

- Connect test box to Engine Control Module of the Engine Control Module; wiring harness is not connected.

- Check central terminal resistance in ECM:

- Connect multimeter between sockets 58 and 60 on the test box for resistance measurement.

• Specification: 60 to 72 ohms

If specification is exceeded or not met:

- Replace engine control module.

If specification is obtained:

- Disconnect test box from Engine Control Module (ECM).

- Connect test box to control module wiring harness.

- Check CAN-data bus wires for short circuit to each other:

- Connect multimeter between test box sockets 58 and 60 for resistance measurement.

• Specification: infinite ohms (no continuity)

- If necessary, repair wire connection according to wiring diagram.

- Check DTC Memory.

- Read out readiness code => [ Readiness Code, Reading ] Monitors, Trips, Drive Cycles and Readiness Codes. If DTC memory was erased, readiness code must be generated => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.