NUT-SQUARE 1956283 - Caterpillar

The CAN data link is used to communicate information between the Electronic Control Module (ECM) and other modules. Use this procedure to troubleshoot any suspect problems with the CAN data link.This procedure identifies the following problems:
Faulty connectors
Missing termination resistors
Short circuits
Open circuits
Faulty display panelA problem with the CAN data link is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness. The next likely cause is a problem with a module that is connected to the data link. The least likely cause is a problem with the ECM.
Illustration 1 g01368886
Schematic for the CAN data link
Illustration 2 g06112342
Connector locations for the CAN data link (typical left side rear engine view)
(1) Engine interface connector
(2) Service tool connector
(3) P1 ECM connector
Illustration 3 g01209797
Terminal locations at the P1 ECM connector that are associated with the CAN data link
(P1-34) CAN data link −
(P1-42) CAN shield
(P1-50) CAN data link +
Illustration 4 g01360095
Terminal locations at the engine interface connector that are associated with the CAN data link
(P1-16) CAN shield
(P1-17) CAN data link +
(P1-18) CAN data link −
Illustration 5 g01209794
Terminal locations at the service tool connector that are associated with the CAN data link
(Terminal C) CAN shield
(Terminal F) CAN data link −
(Terminal G) CAN data link +
Illustration 6 g01355248
Terminal locations at the service tool connector that are associated with the CAN data link
(Terminal C) CAN shield
(Terminal F) CAN data link −
(Terminal G) CAN data link +
Table 1
Troubleshooting Test Step Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Remove the electrical power from the ECM.
B. Thoroughly inspect connectors (1), (2), and (3). Inspect all of the connectors that are associated with 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 the allen head screw on each ECM connector and on the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
E. Check the wiring harnesses for abrasion, for corrosion and for pinch points.
All connectors, pins and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion and of pinch points.
Result: The harness and wiring appear to be OK. Proceed to Test Step 2.
Result: There is a problem in the wiring harness.
Repair the connectors and/or the wiring. Replace parts, if necessary. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled. Verify that the problem is resolved.
2. Verify the Proper Installation of the Termination Resistors
A. Remove the electrical power from the ECM.
B. Disconnect the display panel from the data link.
C. Disconnect the Caterpillar Electronic Technician (ET) from the service tool connector.
D. Disconnect the P1 ECM connector.
Wiggle the harness during the following measurements in order to reveal an intermittent condition.
E. Measure the resistance between terminals P1-50 (CAN Data Link +) and P1-34 (CAN Data Link -).
The resistance is between 57