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.G1526 multimeter or V.A.G1715 multimeter
- V.A.G1594 connector test kit
- Wiring diagram

Test requirements
- A CAN-bus malfunction was recognized via On Board Diagnostic (OBD).
- Data Bus On Board Diagnostic Interface -J533- must be OK.
- Ignition switched off.

Test sequence
Observe safety precautions.
Observe rules for cleanliness.

- Connect 94-pin connector of test box to Engine Control Module (ECM). Test Box, Connecting For Wiring Test

Harness connectors of control module wiring harness are not connected for this.

Checking terminal resistance
- Check terminal resistance in Engine Control Module (ECM) between sockets 67 and 68 of test box.

Specified value: 60.0 to 72.0 Ohms

If specified value is not obtained:
- Replace Engine Control Module (ECM) -J623-.

If specified value is obtained:
- Eliminate malfunction in Data-Bus wires or in other Data-Bus components according to wiring diagram
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes