C4.4 and C6.6 Engines Caterpillar

CAN Data Link - Test

Usage:

C4.4 448

Use this procedure if a fault is suspected in the CAN data links. Also, use this procedure if one of the following diagnostic codes is active:

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Table 1
Diagnostic Trouble Codes for the CAN Data Link Circuit
J1939 Code	CDL Code	Code Description (code descriptions may vary)	Comments
639-9	247-9	J1939 Network #1 : Abnormal Update Rate	Another controller has incorrectly stopped transmitting an expected J1939 message or another controller has incorrectly started transmitting a conflicting J1939 message. The ECM will log the diagnostic code. The engine will not start.
1196-2	1639-2	Anti-theft Component Status States : Erratic, Intermittent, or Incorrect	The Electronic Control Module (ECM) detects poor communications with the Machine Security System (MSS). The engine warning lamp will come on and the ECM will log the diagnostic code. The engine will not start.
1196-9	1639-9	Anti-theft Component Status States : Abnormal Update Rate	The Electronic Control Module (ECM) detects a loss of communications with the Machine Security System (MSS). The warning lamp will come on and the ECM will log the diagnostic code. The engine will not start.
1231-9	2348-9	SAE J1939 Data Link #2 : Abnormal Update Rate	The Electronic Control Module (ECM) detects a loss of communications with the CAN C data link. The warning lamp will come on and the ECM will log the diagnostic code. The engine will not start.

The following background information is related to this procedure:

The CAN data links are also known as J1939 data links. A data link is an industry standard for sending data between different devices in the same application.

High-speed data is transferred via the data links. The data links cannot be accurately tested without complicated equipment. The data links require 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 a J1939 data link is a shielded twisted-pair cable. If the wiring is damaged, the replacement type must be shielded twisted-pair cable.

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Illustration 1	g06101687
Typical example of the schematic for the CAN A data link

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Illustration 2	g06101696
Typical example of the schematic for the CAN B data link

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Illustration 3	g06101703
Typical example of the schematic for the CAN C data link

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Table 2
Troubleshooting Test Steps	Values	Results
1. Use the "System Communication Status to Check the Status of the Other Devices on the Suspect CAN Data Link" A. In the electronic service tool, click the "Diagnostics" tab on the tool bar. B. Select the "System Communication Status" option from the drop-down list.	Component Identified	Result: One or more of the devices on the suspect data link is not visible on the electronic service tool. Repair: Thoroughly inspect the electrical connectors for the suspect devices Refer to Troubleshooting, "Electrical Connectors - Inspect". Check the power supply to the suspect devices. If necessary, refer to Troubleshooting, "Electrical Power Supply - Test". If the fault has been resolved, return the engine to service. If the fault is still present, proceed to Test Step 2. Result: All devices are visible on the electronic service tool. Proceed to Test Step 2.
2. Check the Data Link Terminating Resistance A. Disconnect the P1 and P2 connectors from the ECM. B. Measure the resistance between P1:34 and P1:50. C. Measure the resistance between the P2:21 and P2:29. D. Measure the resistance between the P1:37 and P1:38.	Between 50 Ohms and 70 Ohms	Result: 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 the seals are correctly in place and ensure that the connectors are correctly connected. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair eliminates the fault. Result: The resistance is between 110 and 130 Ohms - one of the terminating resistors may have failed. Repair: Locate the two terminating resistors and remove the two terminating resistors from the harness. Depending on the application, one or both of the terminating resistors may be located in other ECMs on the data link. Measure the resistance of the two terminating resistors. If one of the terminating resistors is incorrect, replace the faulty terminating resistor. If the two terminating resistors are between 110 and 130 Ohms, proceed to Test Step 4. Result: The resistance is greater than 150 Ohms. Proceed to Test Step 3. Result: The resistance is between 50 and 70 Ohms The resistance is correct. The fault may be in the connection to other devices on the data link. Proceed to Test Step 3.
3. Check the Data Link Wiring A. Disconnect each of the connectors that connect other devices on the data link. B. Use a multimeter to measure the resistance between P1:50 and each of the CAN+ pins on other devices on the CAN A data link. C. Use a multimeter to measure the resistance between P1:50 and pin (F) on the diagnostic connector. D. Use a multimeter to measure the resistance between P1:34 and each of the CAN- pins on other devices on the CAN A data link. E. Use a multimeter to measure the resistance between P1:34 and pin (G) on the diagnostic connector. F. Use a multimeter to measure the resistance between P1:29 to each of the CAN+ pins on other devices on the CAN B data link. G. Use a multimeter to measure the resistance between P1:21 to each of the CAN- pins on other devices on the CAN B data link. H. Use a multimeter to measure the resistance between P1:37 to pin 4 on the soot sensor module. I. Use a multimeter to measure the resistance between P1:38 to pin 3 on the soot sensor module.	Less than 2 Ohms	Result: At least one of the resistance measurements is greater than 2 Ohms - there is an open circuit or high resistance in the wiring. Repair: Repair the connectors or the harness and/or replace the connectors or the harness. Ensure that all seals are correctly in place and ensure that the connectors are correctly connected. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair has eliminated the fault. Result: All measured resistances are less than 2 Ohms. Proceed to Test Step 4.
4. Check the Other Devices on the CAN Data Link A. Use the appropriate service tools to diagnose other devices on the data link.	Other devices	Result: At least one of the other devices is not operating correctly. Repair: Use the appropriate service tools to repair other devices on the data link. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair eliminates the fault. Result: The other devices are operating correctly. Contact the Dealer Solutions Network (DSN).