Use this procedure in order to troubleshoot the wiring for the CAN data link.
The CAN data link is used for communication between the following modules: engine's Electronic Control Module (ECM), customer devices and various display modules. Two 120 Ohm terminating resistors must be installed in the wiring harness in order for the CAN data link to function properly.
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| Illustration 1 | g01286073 |
Typical schematic | |
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| Illustration 2 | g01218002 |
P1 ECM connector (P1-50) CAN data link + (P1-34) CAN data link − (P1-42) Shield for the CAN data link | |
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| Illustration 3 | g01234146 |
Location of ECM connectors | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the "main disconnect switch (MDS)" 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 the diagnostic functional test 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 2.
- 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 Resistors
- Verify that the terminating resistors are installed on the ends of the data link.
- Disconnect the J1/P1 ECM connector and measure the resistance between P1-50 (CAN data link +) and P1-34 (CAN data link -).
Expected Result:
The resistance is approximately 60 ± 3 Ohms.
Results:
- OK - The resistance is within the range. Proceed to Test Step 3.
- Not OK - The resistance is approximately 120 ± 6 Ohms. A terminating resistor is missing or damaged.
Repair: If a termination resistor is missing, install the missing resistor. If both resistors are present, measure the resistance between pin A and pin B of the termination resistor. The resistance should measure 120 ± 3 Ohms. Replace the termination resistor if the resistance is not 120 ± 3 Ohms.
STOP
Test Step 3. Check for Shorts in the Harness
- Disconnect any control modules from the CAN data link.
- Disconnect Caterpillar Electronic Technician (ET) from the service tool connector.
- Measure the resistance from P1-50 to every terminal on ECM connectors P1 and P2.
- 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.
- 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. There is a short circuit in the harness or connectors.
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, perform the diagnostic functional test 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