C2.2 Engines For Caterpillar Built Machines Caterpillar

CAN Data Link - Test

Usage:

239D BL9

Use this procedure if a fault is suspected in the CAN data links.

The following background information is related to this procedure:

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

High speed data is transferred via the data links. The data links cannot be accurately tested without complicated equipment. The data links require 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 a 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	g03831199
Schematic for the CAN data link

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Table 1
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 45 N (10 lb) pull test on each of the wires that are associated with the CAN data link. d. Check all of 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 Status of the Other Devices on the Suspect CAN Data Link A. Establish communication between the electronic service tool and the ECM. B. Use the electronic service tool to view the status of the other devices on the suspect CAN data link. If necessary, refer to the Electrical Schematic for the application.	Other devices	Result: One or more of the devices on the suspect data link is not visible on the electronic service tool. Repair: Thoroughly inspect the electrical connectors for the suspect devices Refer to Troubleshooting, "Electrical Connectors - Inspect". Check the power supply to the suspect devices. If necessary, refer to Troubleshooting, "Electrical Power Supply - Test". If the fault has been resolved, return the engine to service. If the fault is still present, proceed to Test Step 3. Result: All devices are visible on the electronic service tool. Proceed to Test Step 3.
3. Check the Data Link Terminating Resistance A. Disconnect the P1 connector from the ECM. B. Measure the resistance between the P1:38 and P1:39.	Between 50 Ohms and 70 Ohms	Result: The resistance is less than 50 Ohms - there is a short circuit in the harness. Repair: Repair the connectors or the harness and/or replace the connectors or the harness. Ensure that all of the seals are correctly in place and ensure that the connectors are correctly connected. Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault. Result: The resistance is greater than 150 Ohms. Proceed to Test Step 4. Result: The resistance is between 110 and 130 Ohms The resistance is correct. The fault may be in the connection to other devices on the data link. Proceed to Test Step 4.
4. 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 P1:38 and each of the CAN+ pins on other devices on the CAN data link. C. Use a multimeter to measure the resistance between P1:39 and each of the CAN- pins on other devices on the CAN data link.	Less than two Ohms	Result: At least one of the resistance measurements is greater than two 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 in order to clear all logged diagnostic codes and then verify that the repair has eliminated the fault. Result: All measured resistances are less than two Ohms. Proceed to Test Step 5.
5. Check the Other Devices on the CAN Data Link A. Use the appropriate service tools in order 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 in order to repair other devices on the data link. Use the electronic service tool in order 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 Solutions Network (DSN).