WRENCH AS.- 2020453 - Caterpillar

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.
Illustration 1 g06087808
Schematic for the CAN data link
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 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 the seals are correctly in place and ensure that the connectors are correctly connected.
Use the electronic service tool to clear all logged diagnostic codes and then