C7.1 Engines and Generator Sets Caterpillar

CAN Data Link - Test

Usage:

C7.1 770

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	Comments
639-9	247-9	J1939 Network #1 : Abnormal Update Rate	Another controller has incorrectly stopped transmitting a J1939 speed request (TSC1) or another controller has incorrectly started transmitting a J1939 speed request. 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	J1939 Network #2 : Abnormal Update Rate	An OEM unit has incorrectly stopped transmitting data or the soot sensor has incorrectly started transmitting a data request. 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.

-9 Detected Problems:

ECM 1 is unable to communicate on the data link.

ECM 1 cannot communicate with other ECM's on the data link, but can communicate with the service tool. This situation indicates a problem with the data link wiring.

ECM 1 is unable to communicate with ECM 2 on the data link.

ECM 1 cannot communicate with ECM 2, indicating a problem with the data link wiring, power or ground circuit, or ECM 2.

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Illustration 1	g06151330
Typical example of the schematic for the CAN A data link

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Illustration 2	g06151360
Typical example of the schematic for the CAN B data link

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Illustration 3	g06151382
Typical example of the schematic for the CAN C data link

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Illustration 4	g02453576
Typical view of the pin locations on the P1 connector (34) CAN A- (37) CAN C+ (38) CAN C- (50) CAN A+

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Illustration 5	g01980934
Typical view of the pin locations on the P2 connector (21) CAN B- (29) CAN B+ (30) CAN A+ (31) CAN A-

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Check for Associated Diagnostic Trouble Codes A. Establish communication between the electronic service tool and the ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary. B. Download the "Warranty Report" from the engine ECM before performing any troubleshooting or clearing diagnostic trouble codes. Troubleshoot any associated diagnostic codes that are present before continuing with this procedure.	Associated Codes	Result: Another diagnostic trouble code is not active or logged. Proceed to Test Step 2. Result: Another code is active or logged. Repair: Troubleshoot the other codes before continuing with this procedure. Refer to Troubleshooting, "Diagnostic Trouble Codes" to troubleshoot the other diagnostic code.
2. Use the "System Communication Status" to Determine the Communication Issue 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: A -9 or -2 code is active. Repair: Refer to the above -9 detected problems for more information. Proceed to Test Step 3.
3. Check the Power and Ground to the ECM A. Turn the keyswitch to the ON position. B. Measure the voltage between the battery (+) and battery (-) terminals on the wiring harness connector of the ECM. Refer to the appropriate wiring diagram.	Battery Voltage	Result: The voltage is not equal to battery voltage. There is an open or short in the wiring circuit. Repair or replace the wiring circuit as necessary. Refer to the machine-specific schematic for wiring information. Proceed to Test Step 6. Result: The voltage is equal to battery voltage. Proceed to Test Step 4.
4. Check the Resistance of the Data Link A. Turn the keyswitch to the OFF position. B. Measure the data link resistance between the ECM data link (+) wire and the data link (-) wire on the wiring harness connector of the ECM. Refer to the appropriate wiring diagram.	60+/-10 Ohms	Result: The resistance is less than 50 Ohms. There are more than two terminating resistors installed in the wiring harness or a short circuit has been detected. Repair: Repair or replace parts as necessary. Proceed to Test Step 5. Result: The resistance is 60 ±10 Ohms. The terminating resistors are OK. Check the power, ground, and keyswitch (if applicable) supply to each module on the affected data link. Refer to the appropriate wiring diagram. Note: Keyswitch must be in the ON position when checking the power supply. Repair the power or ground supply to the modules if necessary. If the power or ground supply is OK, replace the suspect ECM. Proceed to Test Step 5. Result: The resistance is 120 ±10 Ohms. There is a problem with a terminating resistor. Check the resistance on each terminating resistor. Repair: Replace the failed terminating resistor. Proceed to Test Step 5. Result: The resistance is greater than 130 Ohms. There is a problem with the wiring harness between the ECM and the splice point into the data link wiring. Refer to the appropriate wiring diagram. Repair: Determine the cause of the problem. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved. Proceed to Test Step 5.
5. Use the "Systems Communication Status" to Determine the Communication Issue 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. C. Click the "Load from ECM" button to determine if any devices are not communicating.	Component Identified	Result: The "Systems Communication Status" does not show any communication issues. Return the unit to service. Result: The datalink health monitor shows that there are devices that are not communicating. Contact the Dealer Solutions Network (DSN) for assistance.