Terminal Resistance For CAN-Bus, Checking

Terminal resistance for CAN-Bus, checking

Function

The Engine Control Module (ECM) communicates with all data bus-capable control modules via the controller area network (CAN) data bus.

These data bus-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 data bus is recognized as a malfunction and stored.

Trouble-free operation of the CAN-Bus requires that it have a terminating impedance. A central resistor located in the Engine Control Module (ECM) provides the necessary termination.

Recommended special tools and equipment
- VAG 1526 multimeter or VAG 1715 multimeter
- VAG 1594 connector test kit
- Wiring diagram

Test requirements
- DTC "P0600 Data Bus Powertrain missing message" was detected by the Engine Control Module (ECM).
- Ignition switched off.

Test sequence

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

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

- To do this, measure resistance between test box socket 58 & 60:

Specified value: 60 to 72 Ohms

If resistance value is not in expected range:

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

If resistance value is in expected range:

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

- Connect test box to control module wiring harness.

- Check CAN data bus wires for shorts among one another:

- To do this, perform a resistance measurement between test box sockets 58 & 60:

Specified value: Infinity Ohms

If specified value is obtained (wires have no shorts):

- Eliminate fault in wires according to wiring diagram.