With Generic Scan Tool

Terminal Resistance For CAN-Bus, Checking

Function
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).

Recommended special tools and equipment
- V.A.G 1526 multimeter or V.A.G 1715 multimeter
- V.A.G 1594 connector test kit
- 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). connect test box for wiring test. 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: 60.0 to 72.0 Ohms

If resistance value is not in specified range:
- Replace Motronic Engine Control Module (ECM) -J220-.

If resistance value is in specified range:
- Disconnect test box harness connector 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: Infinite Ohms

If specified value is obtained (wires have no shorts):
- Eliminate malfunction in Data-Bus wires or in other Data-Bus components according to wiring diagram.