Use this procedure to troubleshoot the CAN data link if a problem with the wiring is suspected.
The CAN data link is used for communication between the following modules: engine's Electronic Control Module (ECM), customer devices and various display modules. One 120 Ohm terminating resistor must be installed in the wiring harness in order for the CAN data link to function properly.
 | |
| Illustration 1 | g01265457 |
Typical schematic | |
 | |
| Illustration 2 | g01258173 |
P1 ECM connector (P1-34) CAN data link − (P1-42) Shield for the CAN data link (P1-50) CAN data link + | |
 | |
| Illustration 3 | g01265482 |
Machine interface connector (Terminal 18) CAN data link − (Terminal 16) Shield for the CAN data link (Terminal 17) CAN data link + | |
 | |
| Illustration 4 | g01234146 |
Location of ECM connectors | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the breaker for the ECM to the OFF position.
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the connectors to other modules on the CAN data link. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
- Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All of the connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The harness and connectors appear to be OK. Proceed to Test Step 3.
- Not OK - The connectors and/or wiring are not OK.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.
STOP
Test Step 2. Verify the Proper Installation of the Terminating Resistor
- Verify that the terminating resistor is installed in the circuit for the CAN data link.
- Disconnect ECM connector J1/P1 at the engine ECM.
- Disconnect any control modules from the CAN data link.
- Disconnect Cat ET from the service tool connector.
- Measure the resistance between P1-50 (CAN data link +) and P1-34 (CAN data link -).
Expected Result:
The resistance is approximately 120 ± 12 Ohms.
Results:
- OK - The resistance is within the range. Proceed to Test Step 3.
- Not OK - The resistance is incorrect.
Repair: If a termination resistor is missing, install the missing resistor. Replace the termination resistor if the resistance is not 120 ± 12 Ohms.
STOP
Test Step 3. Check for Shorts in the Harness
- Measure the resistance from P1-50 to every terminal on ECM connectors P1 and P2 except P1-34.
- Measure the resistance from P1-50 to the chassis ground.
- Measure the resistance from P1-34 to every terminal on ECM connectors P1 and P2 except P1-50.
- Measure the resistance from P1-34 to the chassis ground.
Expected Result:
The resistance measurements indicate an open circuit.
Results:
- OK - The resistance measurements indicate an open circuit. Proceed to Test Step 4.
- Not OK - The resistance measurements do not indicate an open circuit.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 4. Check for an Open in the Harness
- Use a suitable piece of wire to create a short circuit between the data link wires at one of the control modules on the CAN data link.
- Measure the resistance between P1-50 and P1-34.
- Measure the resistance at the connectors of any other control modules.
Expected Result:
The resistance measurement indicates a short circuit.
Results:
- OK - The resistance measurement indicates a short circuit. The CAN data link is OK.
Repair: If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Not OK - The resistance measurement does not indicate a short circuit. There is an open circuit in the harness or connectors.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP