The CAN data link is used to communicate information between the Electronic Control Module (ECM) and other modules. Use this procedure to troubleshoot any suspect problems with the CAN data link.
This procedure identifies the following problems:
- Faulty connectors
- Missing termination resistors
- Short circuits
- Open circuits
- Faulty display panel
A problem with the CAN data link is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness. The next likely cause is a problem with a module that is connected to the data link. The least likely cause is a problem with the ECM.
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| Illustration 1 | g01549393 |
Schematic for the CAN data link | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove the electrical power from the ECM.
- Thoroughly inspect connectors that are associated with the CAN data link. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the CAN data link.
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| Illustration 2 | g01209797 |
Terminals at the P1 ECM connectors that are associated with the CAN data link (P1-34) CAN data link − (P1-42) CAN shield (P1-50) CAN data link + | |
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| Illustration 3 | g01360095 |
Terminals at the engine interface connector that are associated with the CAN data link (P1-16) CAN shield (P1-17) CAN data link + (P1-18) CAN data link − | |
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| Illustration 4 | g01209794 |
Terminals at the service tool connector that are associated with the CAN data link (Terminal C) CAN shield (Terminal F) CAN data link + (Terminal G) CAN data link − | |
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| Illustration 5 | g01355248 |
Terminals at the connector for the termination resistor that are associated with the CAN data link (Terminal A) CAN data link + (Terminal B) CAN data link − (Terminal C) CAN shield | |
- Check the allen head screw on each ECM connector and on the engine interface connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the wiring harnesses for abrasion, for corrosion and for pinch points.
Expected Result:
All connectors, pins and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The harness and wiring appear to be OK. Proceed to Test Step 2.
- Not OK - There is a problem in the wiring harness.
Repair: Repair the connectors and/or the wiring. Replace parts, if necessary. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled. Verify that the problem is resolved.
STOP
Test Step 2. Verify the Proper Installation of the Termination Resistors
- Disconnect the display panel from the data link.
- Disconnect Caterpillar Electronic Technician (ET) from the service tool connector.
- Disconnect the P1 connector from the primary ECM and from the secondary ECM.
- Measure the resistance between terminals P1-50 (CAN Data Link +) and P1-34 (CAN Data Link -).
Note: Wiggle the harness during the following measurements in order to reveal an intermittent condition.
Expected Result:
The resistance is between 57 and 63 Ohms.
Results:
- OK - The resistance is between 57 and 63 Ohms. Proceed to Test Step 3.
- Not OK - The resistance is between 114 Ohms and 126 Ohms. A termination resistor is missing.
Repair: Verify that two termination resistors are connected to the data link. One resistor must be located on each end of the data link. The engine is shipped with one termination resistor that is installed between the ECM and the engine interface connector.Refer to the appropriate electrical schematic in order to determine the missing resistor. Replace the missing resistor. Verify that the problem is resolved.
STOP
- Not OK - The resistance is less than 57 Ohms. There may be a short circuit in the harness. Proceed to Test Step 3.
- Not OK - The resistance is greater than 126 Ohms. There may be an open circuit in the harness. Proceed to Test Step 4.
Test Step 3. Check the Harness for a Short Circuit
- Remove both termination resistors from the CAN data link.
- Disconnect the display panel.
- Measure the resistance between the points that are listed in Table 1. Be sure to wiggle the wires in the harnesses as you make each resistance measurement. The measurements should be taken at the primary ECM and at the secondary ECM.
Show/hide table
Table 1 Resistance Measurements for the CAN Data Link Connector and Terminal Terminal P1-50 (CAN data link +) All of the other terminals on the P1 connector Engine ground P1-34 (CAN data link -) All of the other terminals on the P1 connector Engine ground
Expected Result:
Each check of the resistance indicates an open circuit.
Results:
- OK - Each check of the resistance indicates an open circuit. The harness is not shorted. Proceed to Test Step 4.
- Not OK - At least one check of the resistance does not indicate an open circuit.
Repair: There is a short circuit in a harness. There may be a problem with a connector. Repair the wiring and/or the connector. Replace part, if necessary. Verify that the problem is resolved.
STOP
Test Step 4. Check the Harness for an Open Circuit
- Remove both termination resistors from the CAN data link.
- Fabricate a jumper wire that is long enough to create a test circuit across the connector for the termination resistor. Crimp connector sockets to each end of the jumper wire.
- Use the jumper wire in order to create a short circuit between terminals A and B on the tee's connector for the termination resistor that is located between the P1 ECM connector and the customer connector. This will effectively replace the termination resistor with a short circuit.
- Measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -). The measurements should be taken at the primary ECM and at the secondary ECM.
- Remove the jumper wire.
- Use the jumper wire in order to create a short circuit between terminals A and B on the tee's connector for the termination resistor that is located on the customer's harness after the engine interface connector. This will effectively replace the termination resistor with a short circuit.
- Measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -). The measurements should be taken at the primary ECM and at the secondary ECM.
- Remove the jumper wire from the tee. Connect the termination resistors to the data link.
- Connect the J1/P1 connectors.
Expected Result:
The resistance measurement indicates that a short circuit exists while the jumper wire is in place.
Results:
- OK - A short circuit exists while the jumper wire is in place. There is not an open circuit. Proceed to Test Step 5.
- Not OK - A short circuit does not exist while the jumper wire is in place. There is an open circuit or excessive resistance in the circuit. There may be a problem in a connector.
Repair: Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 5. Check the Display Panel
- Connect the display panel to another engine.
- Operate the engine and monitor the display panel.
Expected Result:
The display panel operates properly.
Results:
- OK - The display panel operates properly on another engine.
Repair: Connect the display panel to the original engine. If the display panel operates correctly, there may be a problem with an electrical connector. Refer to Troubleshooting, "Electrical Connectors - Inspect".If the display panel does not operate correctly on the original engine, there may be a problem with the ECM.It is unlikely that the ECM has failed. Perform this entire procedure again. If the display panel does not operate correctly, replace the ECM. Refer to Troubleshooting, "ECM - Replace ".
STOP
- Not OK - The display panel does not operate properly on another engine.
Repair: Replace the display panel. Verify that the problem is resolved.
STOP