BODY 9J7864 - Caterpillar

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.
Illustration 1 g02511077
Schematic for the CAN A data link
Illustration 2 g02730831
Schematic for the CAN B data link
Illustration 3 g02453617
Pin locations on the P1 connector (34) CAN A- (50) CAN A+
Illustration 4 g01980934
Pin locations on the P2 connector (21) CAN B- (29) CAN B+Test Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF position.
Thoroughly inspect the connectors in the circuit for 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. Refer to Illustration 2.
Check the harness for abrasion and pinch points from the keyswitch to the Electronic Control Module (ECM).Expected Result:All connectors, pins, and sockets are correctly connected. The harness should be free of corrosion, abrasion and/or pinch points.Results:
OK - Proceed to Test Step 2.
Not OK - Repair: Perform the following repair:Repair the connectors and/or the wiring, or replace the connectors and/or the wiring. 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.STOPTest Step 2. Check the Data Link Terminating Resistance
Disconnect the P1 connector and the P2 connector from the ECM.
Measure the resistance between the P1:34 and P1:50.
Measure the resistance between the P2:30 and P2:31.
Measure the resistance between the P2:21 and P2:29.Expected Result:The resistance is between 50 and 70 Ohms.Results:
The resistance is between 50 and 70 Ohms - This is the correct resistance. The fault may be in the connection to other devices on the data link. Proceed to Test Step 3.
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.STOP
The resistance is between 110 and 130 Ohms - One of the terminating resistors may have failed.Repair: