CAN-Bus, checking (through MY 1999): Function

The Engine Control Module (ECM) ( ) communicates with the ABS Control Module ( ) and the Transmission Control Module (TCM) ( ) via a CAN-Bus ( ).

At least two Control Modules capable of CAN-Bus are connected together via two CAN-Bus wires which are twisted together (CAN_High and CAN_Low) and they exchange information (messages). Missing information on the CAN-Bus will be recognized as a DTC by the Engine Control Module (ECM) as well as by other CAN-Bus Control Modules.

Fig 1: CAN-Bus Circuit Diagram

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Two Control Modules have terminal resistors each of 120 Ω, these resistors make sure that the CAN-Bus can function without a malfunction. These terminal resistors are located in the engine and ABS Control Modules.

Special tools, testers and auxiliary items required 

• Test box V.A.G 1598/22 (through my 1999)
• Test box V.A.G 1598/31 (from my 2000)
• Digital multimeter US 1119 (Fluke 83 or equivalent)
• Adapter set V.A.G 1594

• Wiring diagram

Vehicles with manual transmission 

• Test box V.A.G 1598/21

Vehicles with automatic transmission 

• Test box V.A.G 1598/18