Terminal Resistance For CAN-Bus, Checking

Terminal resistance for CAN-bus, vehicles 09.99 >, checking

Function
The Engine Control Module (ECM) communicates with all data bus-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 data bus 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
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements
- A CAN-bus malfunction was recognized via On Board Diagnostic (OBD)
- Ignition switched off.

Test sequence
- Connect test box to Transmission Control Module (TCM) wiring harness.

- Check the central termination resistor in the Engine Control Module (ECM).

- To do this, measure resistance between test box socket 3 + 25.
Specified value: 55.0 - 75.0 Ohms

If specified value is not obtained:
- Remove wiper arms and wind cowl.
- Disengage connector from Engine Control Module (ECM) and disconnect it.

- Check CAN-Bus wires at test box (V.A.G 1598/18A) between sockets 3 + 25 for short circuit to each other.
Wire resistance: infinite ohms

If a malfunction is detected in the wires (wires have a short circuit to each other):
- Eliminate error in wires (see circuit diagram)
- Erase DTC memory of Engine Control Module (ECM).
- Generate readiness code.

If no malfunction is detected in the wires (wires have no short circuit to each other):
- Connect test box to Engine Control Module (ECM) wiring harness.
- Check CAN-Bus wires between Motronic Engine Control Module (ECM) -J220- and Transmission Control Module (TCM) -J217- for open circuit according to wiring diagram.
Wire resistance: max. 1.5 ohms






If a malfunction is found in wires:
- Eliminate error in wires (see circuit diagram)
- Erase DTC memory of Engine Control Module (ECM).
- Generate readiness code.

If no malfunctions are found in wires:
- Replace Motronic Engine Control Module (ECM) -J220-.