Use this procedure to troubleshoot the electrical system if a problem is suspected with the CAN data link or the Cat Data Link. Also, use this procedure if the diagnostic code in Table 1 is active or easily repeated.
| Diagnostic Trouble Codes | ||
|---|---|---|
| J1939 Code and Description | Conditions that Generate the Code | System Response |
| 639-9 J1939 Network #1 : Abnormal Update Rate | The Electronic Control Module (ECM) has lost all communications with the transmission ECM over the Cat Data Link. | The code is logged. |
Note: This procedure checks for an open or for a short in the data link circuits.
If Caterpillar Electronic Technician (ET) will not communicate with the ECM, refer to Troubleshooting, "Electronic Service Tool Does Not Communicate" before you begin this procedure. The procedure will verify that electrical power is being supplied to the ECM and to the service tool connector.
The data links are used to communicate information between the engine ECM and other control modules that are a part of the application. Cat ET also communicates with the ECM via the data links.
The service tool connector contains connections for electrical power and for the data links.
When the keyswitch is in the OFF position, Cat ET may communicate with the ECM. However, the communications may be disrupted and the communications may require frequent reconnection. In order to avoid this problem, place the keyswitch in the ON position when Cat ET is being used.
Cat ET may display the following error message:
"The version of the ECM is not recognized and the integrity of the changed parameters and displayed data is not guaranteed."
This message indicates that one of the following conditions exist:
- The flash file in the ECM is newer than the version of Cat ET.
- The latest version of Cat ET has not been installed.
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| Illustration 1 | g02138795 |
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Schematic for the Cat Data Link | |
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| Illustration 2 | g01672679 |
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Terminal locations at the service tool connector (Terminal A) +Battery (Terminal B) −Battery (Terminal C) CAN shield (Terminal D) Cat Data Link + (Terminal E) Cat Data Link − (Terminal F) CAN data link − (Terminal G) CAN data link + | |
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| Illustration 3 | g01672676 |
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Terminal locations at the P1 ECM connector that are for the data link (P1-8) Cat Data Link + (P1-9) Cat Data Link − (P1-34) CAN data link − (P1-42) CAN shield (P1-48) +Battery (P1-50) CAN data link + (P1-52) +Battery (P1-53) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-70) Keyswitch | |
Test Step 1. Check for a Short Circuit
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the connectors that are associated with the data link circuits. Refer to Troubleshooting, "Electrical Connectors - Inspect".
- Disconnect the J1/P1 ECM connectors.
- Disconnect Cat ET from the service tool connector.
- 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.
Show/hide table
Table 2 Resistance Measurements for the Cat Data Link Connector and Terminal Terminal P1-8 (Cat Data Link +) All of the other terminals on the P1 connector Negative ground P1-9 (Cat Data Link -) All of the other terminals on the P1 connector Negative ground P1-50 (CAN data link +) All of the other terminals on the P1 connector Negative ground P1-34 (CAN data link -) All of the other terminals on the P1 connector Negative ground
Expected Result:
Each check of the resistance indicates an open circuit.
Results:
- OK - Each check of the resistance indicates an open circuit. Proceed to Test Step 2.
- Not OK - At least one check of the resistance does not indicate an open circuit. There is a short circuit in the harness or in a connector.
Repair: Repair the connectors and/or the wiring. Replace parts, if necessary. Verify that the original problem is resolved.
STOP
Test Step 2. Check for an Open Circuit
- Fabricate a jumper wire that is long enough to create a test circuit across two terminals at the harness connector. Crimp connector sockets to each end of the jumper wire.
- Use the jumper wire to create a short between terminals D (Cat Data Link +) and E (Cat Data Link −) at the service tool connector.
- Measure the resistance between P1-8 (Cat Data Link +) and P1-9 (Cat Data Link −).
- Use the jumper wire to create a short between terminals G (CAN data link +) and F (CAN data link −) at the service tool connector.
- Measure the resistance between P1-50 (Cat Data Link +) and P1-34 (Cat Data Link −).
Expected Result:
Each of the resistance measurements indicate a short circuit.
Results:
- OK - Each of the resistance measurements indicate a short circuit. Remove the jumper wire from the service tool connector. Proceed to Test Step 3.
- Not OK - At least one of the resistance measurements indicates an open circuit.
Repair: Remove the jumper wire from the ECM connector. Determine the cause of the open circuit. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 3. Check the Termination Resistors for the CAN Data Link
Note: Perform this test only if you are troubleshooting a problem with the CAN data link.
- At the service tool connector, measure the resistance between the terminals for the CAN data link.
Expected Result:
The resistance of the data link is between 45 Ohms and 75 Ohms.
Results:
- OK - The resistance is between 45 Ohms and 75 Ohms.
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 test procedure again. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems.
STOP
- Not OK - The resistance is approximately 120 Ohms. There is a problem with a termination resistor. At least one measurement is less than five Ohms. The wiring for a data link has a short circuit.
Repair: Determine the cause of the missing termination resistor. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
- Not OK - The resistance is greater than 140 ohms. There is a problem with both termination resistors.
Repair: Determine the cause of the problem. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP