C7 and C9 Industrial Engines 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 covers the 247-09 J1939 Data Link communications.

This procedure identifies the following problems:

• Faulty connectors

• Missing termination resistors

• Short circuits

• Open circuits

• Faulty J1939 display

Illustration 1	g01119843
Schematic for the CAN data link

Illustration 2	g01167488
Engine view (typical example) (1) J1/P1 ECM connectors

Illustration 3	g01149983
Engine view (typical example) (2) J61 customer connector (3) J63 service tool connector

Illustration 4	g01215698
P1 terminals that are associated with the CAN data link (P1-34) CAN data link − (P1-42) CAN shield (P1-50) CAN data link +

Illustration 5	g01123351
J61/P61 terminals that are associated with the CAN data link (16) CAN shield (17) CAN data link + (18) CAN data link −

Table 1

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the keyswitch to the OFF position. B. Thoroughly inspect connectors (1), (2), and (3). Thoroughly inspect the connectors for each module that is connected to the CAN data link. Refer to Troubleshooting, "Electrical Connectors - Inspect". 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 for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value. E. Check the allen head screw on the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value. F. Check the wiring harnesses for abrasion, for corrosion and for pinch points.	Connectors and Wiring	Results: The harness and the wiring appear to be OK. Proceed to Test Step 2. Results: There is a problem in the wiring harness. Repair: 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 coupled. Verify that the problem is resolved. STOP
2. Check for Codes A. Connect Cat® Electronic Technician to the service tool connector. B. Turn the keyswitch to the ON position. C. Observe the active diagnostic code screen on Cat ET. Wait at least 15 seconds so that any diagnostic codes may become active. Check for a 247-09 diagnostic code.	Codes	Results: No codes are active. Repair: The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect". STOP Results: A 247-09 diagnostic code is active. Proceed to Test Step 3.
3. Verify the Proper Installation of the CAN Data Link A. Disconnect the J1939 display. B. Disconnect the P1 connector and measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -).	CAN Data Link	Results: The resistance is between 57 and 63 Ohms. Proceed to Test Step 6. Results: The resistance is between 114 Ohms and 126 Ohms. A terminating resistor is missing. Repair: Verify that two terminating resistors exist on the data link. One resistor must be located on each end of the data link. If the optional harness is ordered with the engine, the engine is shipped with one terminating resistor that is installed between the ECM and the customer connector. Refer to the appropriate electrical schematic in order to determine the missing resistor. Replace the missing resistor. Verify that the problem is resolved. STOP Results: The resistance is less than 57 Ohms. Proceed to Test Step 4. Results: The resistance is greater than 126 Ohms. Proceed to Test Step 5.
4. Check for a Short Circuit A. Disconnect the J1/P1 ECM connector. B. Remove the terminating resistors from the CAN data link. C. If a J1939 display is installed, disconnect the display. D. Measure the resistance between the points that are listed in Table 2. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.	Short Circuit	Results: Each check of the resistance indicates an open circuit. Proceed to Test Step 5. Results: At least one check of the resistance does not indicate an open circuit. There is a short circuit in a harness. There may be a problem with a connector. Repair: Repair the wiring and/or the connector. Replace part, if necessary. Verify that the problem is resolved. STOP

Table 2

Resistance Measurements for the CAN Data Link
Connector and Terminal	Terminal
P1-50 (CAN data link +)	All of the other terminals on the P1 connector
	Engine ground
P1-34 (CAN data link -)	All of the other terminals on the P1 connector
	Engine ground

Table 3

Troubleshooting Test Steps	Values	Results
5. Check for an Open Circuit A. Verify that all of the connections are disconnected. B. Fabricate a jumper wire. Use the jumper wire in order to create a short circuit between terminals G and F on the service tool connector. C. Measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -). D. Remove the jumper wire from the service tool connector.	10 Ohms	Results: The resistance is less than ten Ohms. There is not an open circuit. Proceed to Test Step 6. Results: The resistance is more than ten Ohms. There is an open circuit or excessive resistance in the circuit. There may be a problem in a connector. Repair: Repair the wiring and/or the connector. Replace part, if necessary. Verify that the problem is resolved. STOP
6. Check the J1939 Display A. Connect the J1939 display to another engine. B. Operate the engine and monitor the J1939 display.	J1939 Display	Results: The J1939 display operates properly on another engine. Repair: Connect the display to the original engine. If the display operates correctly, there may be a problem with an electrical connector. Refer to Troubleshooting, "Electrical Connectors - Inspect". If the display does not operate correctly on the original engine, there may be a problem with the ECM.It is unlikely that the ECM has failed. Perform this entire procedure again. Replace the ECM if the display does not operate correctly. Refer to Troubleshooting, "ECM - Replace". Results: The J1939 display does not operate properly on another engine. Repair: Replace the J1939 display. Verify that the problem is resolved. STOP