Can-Bus, Checking Terminal Resistance

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).

Special tools and workshop equipment required

Multimeter VAG1526 or multimeter VAG1715
Connector test kit VAG1594
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), connect test box for wiring test. During this, wiring harness to Engine Control Module (ECM) is not connected.

-- Check the 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 Ω

If resistance value is not in specified range:

-- Replace Motronic Engine Control Module (ECM) -J220- ENGINE CONTROL MODULE, REPLACING .

If resistance value is in specified range:

-- Eliminate malfunction in Data-Bus wires or in other Data-Bus components according to wiring diagram: Refer to SYSTEM WIRING DIAGRAM