SEAL-BUFFER 2017747 - Caterpillar

Use this procedure to troubleshoot the CAN data link circuit if a problem is suspected.
Illustration 1 g03318854
Typical schematic
Illustration 2 g03322947
Terminal locations at the P1/J1 connector
(P1-34) CAN data link -
(P1-42) CAN data link shield
(P1-50) CAN data link +
Illustration 3 g03322964
Terminal locations at the service tool connector
(Terminal C) CAN data link shield
(Terminal F) CAN data link -
(Terminal G) CAN data link +
Illustration 4 g03322965
Terminal locations at the customer connector
(Terminal 35) CAN data link +
(Terminal 36) CAN data link -
(Terminal 38) CAN data link shield The CAN data link is used for communication between the following modules: the engine 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.
Table 1
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Remove electrical power from the ECM.
B. Thoroughly inspect the electrical connectors for the CAN data link circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the proper procedure for inspecting the connectors and the wiring.
Electrical Connections
Results: The connectors and wiring appear to be OK.
Proceed to Test Step 2.
Result: There is a problem in the connectors and/or wiring.
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 coupled.
Verify that the repair eliminated the problem.
2. Verify the Proper Installation of the Terminating Resistors
A. Verify that the terminating resistors are installed at the ends of the data link.
B. Disconnect the J1/P1 connector and measure the resistance between P1-50 (CAN data link +) and P1-34 (CAN data link -).
60 3 Ohms
Results: The resistance is within the range.
Repair: The termination resistors are OK. The data link appears to be OK. The problem is probably an intermittent problem in a connector or in the harness. If the problem persists, perform this procedure again. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems.
Proceed to Test Step 3.
Results: The resistance is approximately 120 Ohms. There is a problem with a termination resistor.
Repair: Determine the cause of the missing termination resistor. Repair the problem, when possible. Replace parts, if necessary.
Verify that the repair eliminated the problem.
3. Check for Shorts in the Harness
A. Disconnect the J1/P1 ECM connector at the ECM.
B. Disconnect any control modules from the CAN data link.
C. Disconnect Cat ET from the service tool connector.
D. Measure the resistance from the P1-50 terminal to every terminal on ECM connectors P1 and P2.
E. Measure the resistance from P1-50 to the chassis ground.
F. Measure the resistance from P1-34 to every terminal on ECM connectors P1 and P2.
G. Measure the resistance from P1-34 to the chassis ground.
Open Circuit
Results: Each measurement indicates an open circuit. The wiring for the data link does not have a short circuit.
Proceed to Test Step 4.
Results: The resistance measurements do not indicate an open circuit.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
4. Check for an