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 covers the 247-09 J1939 Data Link communications.
This procedure identifies the following problems:
- Faulty connectors
- Missing termination resistors
- Short circuits
- Open circuits
- Faulty J1939 display
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| Illustration 1 | g01175308 |
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Schematic for the CAN data link | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
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Illustration 2 g01146374 Engine view (typical example)
(1) J1/P1 ECM conntctorsShow/hide table
Illustration 3 g01149983 Engine view (typical example)
(2) J61 customer connector
(3) J63 service tool connector - Thoroughly inspect connectors (1), (2), and (3). Thoroughly inspect the connectors for each module that is connected to the CAN data link. Refer to Troubleshooting, "Electrical Connectors - Inspect".
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Illustration 4 g01102141 P1 terminals that are associated with the CAN data link
(P1-34) CAN data link −
(P1-42) CAN shield
(P1-50) CAN data link +Show/hide table
Illustration 5 g01123351 J61/P61 terminals that are associated with the CAN data link
(16) CAN shield
(17) CAN data link +
(18) CAN data link − - Perform a
45 N (10 lb) pull test on each of the wires that are associated with the CAN data link. - Check the allen head screw on each ECM connector for the proper torque. Also, check the allen head screw on the customer 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 the 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. Check for Active Diagnostic Codes
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
- Turn the keyswitch to the ON position.
- Observe the active diagnostic code screen on Cat ET. Wait at least 15 seconds so that any diagnostic codes may become active. Check for a 247-09 diagnostic code.
Expected Result:
No diagnostic codes are active.
Results:
- OK - No codes are active.
Repair: The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Not OK - A 247-09 diagnostic code is active. Proceed to Test Step 3.
Test Step 3. Verify the Proper Installation of the CAN Data Link
- Disconnect the J1939 display.
- Disconnect the P1 connector and measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -).
Expected Result:
The resistance is between 57 and 63 Ohms.
Results:
- OK - The resistance is between 57 and 63 Ohms. Proceed to Test Step 6.
- Not OK - The resistance is between 114 Ohms and 126 Ohms. A terminating resistor is missing.
Repair: Verify that two terminating resistors exist on the data link. One resistor must be located on each end of the data link. The engine is shipped with one terminating resistor that is installed between the ECM and the customer 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. Proceed to Test Step 4.
- Not OK - The resistance is greater than 126 Ohms. Proceed to Test Step 5.
Test Step 4. Check for a Short Circuit
- Disconnect the J1/P1 ECM connector.
- Remove the terminating resistors from the CAN data link.
- If a J1939 display is installed, disconnect the display.
- 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.
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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. Proceed to Test Step 5.
- Not OK - At least one check of the resistance does not indicate an open circuit. There is a short circuit in a harness. There may be a problem with a connector.
Repair: Repair the wiring and/or the connector. Replace part, if necessary. Verify that the problem is resolved.
STOP
Test Step 5. Check for an Open Circuit
- Verify that all of the connections are disconnected.
- Fabricate a jumper wire. Use the jumper wire in order to create a short circuit between terminals G and F on the service tool connector.
- Measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -).
- Remove the jumper wire from the service tool connector.
Expected Result:
The resistance is less than ten Ohms.
Results:
- OK - The resistance is less than ten Ohms. There is not an open circuit. Proceed to Test Step 6.
- Not OK - The resistance is more than ten Ohms. 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 part, if necessary. Verify that the problem is resolved.
STOP
Test Step 6. Check the J1939 Display
- Connect the J1939 display to another engine.
- Operate the engine and monitor the J1939 display.
Expected Result:
The J1939 display operates properly.
Results:
- OK - The J1939 display operates properly on another engine.
Repair: Connect the display to the original engine. If the display operates correctly, there may be a problem with an electrical connector. Refer to Troubleshooting, "Electrical Connectors - Inspect".
If the display 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. Replace the ECM if the display does not operate correctly. Refer to Troubleshooting, "Replacing the ECM".
STOP
- Not OK - The J1939 display does not operate properly on another engine.
Repair: Replace the J1939 display. Verify that the problem is resolved.
STOP