CAN-Bus Terminal Resistance, TCM to ECM, Checking
CAN-Bus Terminal Resistance, TCM to ECM, Checking
The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) 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 Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248).
Special tools, testers and auxiliary items required
• Multimeter.
• Wiring diagram.
Test requirement
• A CAN-Bus malfunction was recognized.
• The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) fuses OK.
• Battery voltage at least 12.5 V.
• Ignition switched off.
Test procedure
- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check
Start diagnosis
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 -.
- Pull the Transmission Control Module (TCM) (J217 ) electrical harness electrical connector - 1 - retaining tab in the direction of the - arrow - and remove from the Transmission Control Module (TCM) (J217) - 2 -.
- Remove the retaining nuts - 3 - and the Transmission Control Module (TCM) (J217) - 2 - in the direction of the - arrow -.
• The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) must remain connected for the following step.
- Using a Multimeter, check the Transmission Control Module (TCM) (J217) electrical harness connector T68 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, loose 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 ] .
If the specified value was obtained:
Checking wiring
If the manufacturers test box is being used, perform the following step.
- Install the Adapter F/VAG1598 (68 Pin) (VAG1598/22 )
- Install the Adapter - 68 Pin (VAG1598/18).
If the manufacturers test box is not being used, perform the following step.
- Remove the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
- Using a Multimeter, check the Transmission Control Module (TCM) (J217) electrical harness connector T68 to the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) electrical harness connector T80 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, loose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory
- Perform a road test to verify repair.
If the DTC does not return:
Repair complete, Generate readiness code. Refer to => [ Readiness Code ] Readiness Code.
- End diagnosis.
If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:
- Replace the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
- Assembly is performed in the reverse of the removal.
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.