C3.4B Engines CAN Data Link - Test Caterpillar

CAN Data Link - Test

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C3.4B Engines CAN Data Link - Test

Use this procedure if a fault is suspected in the CAN data link. This procedure also covers the following diagnostic codes:

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Table 1
Diagnostic Trouble Codes for the CAN Data Link
J1939 Code	Description	Notes
639-9	J1939 Network #1 : Abnormal Update Rate	The ECM detects that another controller has incorrectly stopped transmitting a J1939 speed request (TSC1) or another controller has incorrectly started transmitting a J1939 speed request. The warning lamp will come on.
639-14	J1939 Network #1 : Special Instruction	Another controller has incorrectly stopped transmitting a signal on the CAN 1 data link. The warning lamp will come on. The engine limp home strategy will be enabled.
1231-9	J1939 Network #2 : Abnormal Update Rate	The ECM has detected that the CAN 2 data link is not functioning. The warning lamp will come on.

The following background information is related to this procedure:

The CAN data link is also known as J1939 data link. The data link is an industry standard for sending data between different devices in the same application.

High-speed data is transferred via the data link. The data link cannot be accurately tested without complicated equipment. The data link requires a resistance of 60 Ohms between the two wires to transmit the data correctly. This resistance is made up of two 120 Ohm resistors. The two resistors are known as "Terminating Resistors". The terminating resistors should be at opposite ends of a data link circuit. If this resistance is not present, then the data will be intermittent or unreadable.

Note: The wiring for the J1939 data link is a shielded twisted-pair cable. If the wiring is damaged, the replacement type must be shielded twisted-pair cable.

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Illustration 1	g03717599
Schematic diagram of the CAN 1 datalink Not all connectors are shown. Refer to the Electrical Schematic for the application.

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Illustration 2	g03717152
Schematic diagram of the CAN 2 datalink Not all connectors are shown. Refer to the Electrical Schematic for the application.

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Illustration 3	g03717619
Typical view of the pin locations on the P1 connector (23) CAN 2 + (45) CAN 2 - (46) CAN 1 + (47) CAN 1 -

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Table 2
Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Turn the keyswitch to the OFF position. B. Inspect the connectors in the circuit for the CAN data link. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Perform a 30 N (6.7 lb) pull test on each of the wires that are associated with the CAN data link. D. Check all the wiring associated with the CAN data link for abrasions and pinch points.	Damaged wire or connector	Result: A damaged wire or damaged connector was found. Repair: Repair the damaged wire or the damaged connector. Use the electronic service tool to clear all logged diagnostic codes. Verify that the repair eliminates the fault. Result: A damaged wire or damaged connector was not found. Proceed to Test Step 2.
2. Check the Data Link Terminating Resistor in the Harness A. Disconnect the data link terminating resistors from the harness. B. Measure the resistance of the resistors.	120 Ohms	Result: The resistance is not 120 Ohms. Repair: Replace the suspect terminating resistor. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair eliminates the fault. Result: The resistance is 120 Ohms. Proceed to Test Step 3.
3. Check the Data Link Terminating Resistor in the ECM A. Disconnect the P1 connector from the ECM. B. Measure the resistance between J1:46 and J1:47. C. Measure the resistance between J1:23 and J1:45.	120 Ohms	Result: The resistance is not 120 Ohms. The terminating resistor inside the ECM is faulty. Repair: Replace the ECM. Refer to Troubleshooting, ECM - Replace. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair eliminates the fault. Result: The resistance is 120 Ohms. Proceed to Test Step 4.
4. Check the Resistance of the Harness A. Disconnect the P1 connector. B. Measure the resistance between P1:46 and P1:47. C. Measure the resistance between P1:23 and P1:45.	Between 110 Ohms and 130 Ohms.	Result: The resistance is less than 110 Ohms. There is a short in the data link wiring. Replace the data link wiring. Use the electronic service tool to verify that the repair eliminates the fault. Result: The resistance is greater than 130 Ohms. Proceed to Test Step 5. Result: The resistance is between 110 Ohms and 130 Ohms. Proceed to Test Step 6.
5. Check the Data Link Wiring A. Disconnect each of the connectors that connect other devices on the data link. B. Use a multimeter to measure the resistance between P1:46 and each of the CAN 1 + pins for other devices on the CAN 1 data link. Use a multimeter to measure the resistance between P1:23 and each of the CAN 2 + pins for other devices on the CAN 2 data link. C. Use a multimeter to measure the resistance between P1:46 and pin F on the diagnostic connector. D. Use a multimeter to measure the resistance between P1:47 and each of the CAN 1 - pins for other devices on the CAN 1 data link. Use a multimeter to measure the resistance between P1:45 and each of the CAN 2 - pins for other devices on the CAN 2 data link. E. Use a multimeter to measure the resistance between P1:47 and pin G on the diagnostic connector.	Less than 5 Ohms	Result: At least one of the resistance measurements is greater than 5 Ohms - there is an open circuit or high resistance in the wiring. Repair: Repair the connectors or the harness and/or replace the connectors or the harness. Ensure that all seals are correctly in place and ensure that the connectors are correctly connected. Use the electronic service tool toclear all logged diagnostic codes and then verify that the repair has eliminated the fault. Result: All measured resistances are less than 5 Ohms. Proceed to Test Step 6.
6. Check the Other Devices on the CAN Data Link A. Use the appropriate service tools to diagnose other devices on the data link.	Other devices are OK	Result: At least one of the other devices is not operating correctly. Repair: Use the appropriate service tools to repair other devices on the data link. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair eliminates the fault. Result: The other devices are operating correctly. Contact the Dealer Solution Network (DSN).