Terminal Resistance for CAN-Bus, Checking

Function 

The Engine Control Modules communicate with all databus-capable control modules via a CAN-Bus.

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 corresponding Engine Control Module.

Test Conditions 

• A CAN-bus malfunction was recognized via On Board Diagnostic, Diagnostic mode 3: Check DTC memory.
• Ignition switched off.

Special tools, testers and auxiliary items required 

• Hand multimeter V.A.G 1526 or Multimeter V.A.G 1715
• Test adapter kit V.A.G 1594
• Wiring diagram

Test Sequence 

• Connect test box to the corresponding Engine Control Module, connecting test box for wiring test. The control module wiring harness is not connected.
• Check central terminal resistance in Engine Control Module:
• Measure resistance between test box sockets 58 +60: Specification: 115 to 135 Ω

If resistance value is not in specified range: 

Replace the engine control module.

If resistance value is in specified range: 

• Eliminate malfunction in CAN-Bus wires or in other CAN-Bus components according to wiring diagram: Electrical Wiring Diagrams, Troubleshooting and Component Locations
• Erase DTC memory of Engine Control Module → Diagnostic Mode 04 - Erase DTC Memory , Diagnostic mode 4: Reset/erase diagnostic data.
• Generate readiness code → Readiness Code, Generating .