CAN-Bus Terminal Resistance, TCM to ECM, Checking
CAN-Bus Terminal Resistance, TCM to ECM, Checking
The Motronic Engine Control Module (ECM) (J220) 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. The central terminal resistor is located in the Engine Control Module (ECM) (J220).
Special tools, testers and auxiliary items required
• Multimeter.
• Wiring diagram.
Test requirement
• A CAN-Bus malfunction was recognized.
• The Engine Control Module (ECM) (J220) fuses OK.
• Battery voltage at least 12.5 V.
• Ignition switched off.
Removal
- Remove the center dash panel - 1 - in the direction of the - arrow -.
- Remove the right upper dashboard panel.
- Remove the three center screws - 1 -
- Remove the right upper dashboard panel - 1 - in the direction of - arrow A - and - arrow B -.
- Remove the retaining screw - arrow -.
• The Engine Control Module (ECM) (J220) must remain connected for the following step.
- Using a Multimeter, check the Transmission Control Module (TCM) (J217) electrical harness connector terminals 3 to 25 for resistance.
Specified value: 60 to 72 ohms (at approx. 20° C)
If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
- Replace the Engine Control Module (ECM) (J220 ). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
If the specified value was obtained:
Checking wiring
- Install the Adapter F/VAG1598 (68 Pin) (VAG1598/22 ). Refer to Automatic Transmission Repair Information.
If the manufacturers test box is not being used, perform the following step.
- Remove the Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
- Using a Multimeter, check the Transmission Control Module (TCM) (J217) electrical harness connector to the Engine Control Module (ECM) (J220) electrical harness connector T94 for resistance.
Specified value: 1.5 ohms Max.
If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
- Replace the Transmission Control Module (TCM) ( J217). Refer to => [ Transmission Control Module, Replacing ] Transmission Control Module, Replacing.
Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.
2. If necessary, erase the DTC memory. => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.
3. If the DTC memory was erased, generate readiness code. => [ Readiness Code ] Readiness Code.
- End of diagnosis.