Terminal Resistance For CAN-Bus, Checking

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), connecting test box for wiring test. Test Box, Connecting 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