PLATE 7M0659 - Caterpillar

Use this procedure to troubleshoot the CAN data link if a problem with the wiring is suspected. The CAN data link is used for communication between the following modules: engine's Electronic Control Module (ECM), customer devices and various display modules. Two 120 Ohm terminating resistors must be installed in the wiring harness in order for the CAN data link to function properly.
Illustration 1 g01386933
Typical schematic
Illustration 2 g01381785
P1 ECM connector
(P1-34) CAN data link −
(P1-42) Shield for the CAN data link
(P1-50) CAN data link +
Illustration 3 g01381831
Customer connector
(Terminal 32) CAN data link −
(Terminal 33) Shield for the CAN data link
(Terminal 35) CAN data link +
Illustration 4 g01381854
Service tool connector
(Terminal C) Shield for the CAN data link
(Terminal F) CAN data link −
(Terminal G) CAN data link +
Illustration 5 g01234146
Location of ECM connectors
Test Step 1. Inspect the Electrical Connectors and the Wiring
Turn the main disconnect switch to the OFF position.
Thoroughly inspect the ECM connector J1/P1. Inspect all of the connectors to other modules on the CAN data link. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and the wiring for abrasion and for pinch points. Expected Result:All of the connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.Results:
OK - The harness and connectors appear to be OK. Proceed to Test Step 3.
Not OK - The connectors and/or wiring are not OK.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.STOPTest Step 2. Verify the Proper Installation of the Terminating Resistors
Verify that the terminating resistors are installed on the ends of the data link.
Disconnect the J1/P1 ECM connector and measure the resistance between P1-50 (CAN data link +) and P1-34 (CAN data link -). Expected Result:The resistance is approximately 60 3 Ohms.Results:
OK - The resistance is within the range. Proceed to Test Step 3.
Not OK - The resistance is approximately 120 6 Ohms. A terminating resistor is missing or damaged.Repair: If a termination resistor is missing, install the missing resistor. If both resistors are present, measure the resistance between pin A and pin B of the termination resistor. The resistance should measure 120 3 Ohms. Replace the termination resistor if the resistance is not 120 3 Ohms.STOPTest Step 3. Check for Shorts in the Harness
Disconnect the ECM connector J1/P1 at the engine ECM.
Disconnect the ECM connector J2/P2 at the engine ECM.
Disconnect any control modules from the CAN data link.
Disconnect Caterpillar Electronic Technician (ET) from the service tool connector.
Measure the resistance from P1-50 to every terminal on ECM connectors P1 and P2.
Measure the resistance from P1-50