Note: This procedure checks for an open circuit or for a short circuit in the Cat Data Link. If you are experiencing problems with communications between the Caterpillar Electronic Technician (ET) and the Electronic Control Module (ECM), refer to the troubleshooting without a diagnostic code procedure Troubleshooting, "Electronic Service Tool Will Not Communicate with ECM" before you use this procedure.
The Cat Data Link is the standard data link that is used by the ECM to communicate with Cat ET. The ECM communicates with Cat ET in order to share status information and diagnostic information. Cat ET can also be used to configure the ECM parameters. This information will not be available if communication fails between the ECM and Cat ET.
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Schematic for the Cat Data Link | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the battery isolator switch to the OFF position.
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Illustration 2 g01141049 Location of the J1/P1 ECM connectors (typical left side engine view) - Thoroughly inspect the J1/P1 ECM connectors. Also, thoroughly inspect the service tool connector. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".
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Illustration 3 g01240936 P1 terminals that are associated with the Cat Data Link
(P1-8) Cat Data Link +
(P1-9) Cat Data Link −Show/hide table
Illustration 4 g01200543 Terminals at the service tool connector that are associated with the Cat Data Link
(D) Cat Data Link +
(E) Cat Data Link − - Perform a
45 N (10 lb) pull test on each of the wires that are associated with the Cat Data Link. - Check the allen head screw on each ECM connector for the proper torque. Also, check the allen head screw on the customer connector for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
Expected Result:
All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK - The harness and the connectors appear to be OK. Proceed to Test Step 2.
- Not OK - The connectors and/or the wiring are not OK.
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 completely coupled. Verify that the original problem is resolved.
STOP
Test Step 2. Check the Data Link for a Short Circuit
- Disconnect the J1 connector.
- Disconnect Cat ET from the service tool connector.
- Measure the resistance between the points that are listed in Table 1. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
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Table 1 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 Ground stud P1-9 (Cat Data Link -) All of the other terminals on the P1 connector Ground stud
Expected Result:
Each check of the resistance indicates an open circuit.
Results:
- OK - Each check of the resistance indicates an open circuit. The data link is not shorted to another wire that is in the harness. Proceed to Test Step 3.
- 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 3. Check the Data Link for an Open Circuit
- Fabricate a jumper wire that can be used to short two terminals at the service tool connector. Crimp connector pins to each end of the jumper wire. Use the jumper wire in order to create a short circuit 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 −) at the ECM connector.
Expected Result:
Resistance indicates that a short circuit condition exists.
Results:
- OK - Resistance indicates a short circuit.
Repair: The data link does not have an open in the harness. Perform the following procedure:
- Connect the J1/P1 connectors. Connect Cat ET to the service tool connector.
- Use Cat ET to check that communications can be established over the Cat Data Link. If Cat ET is unable to communicate over the data link, there may be a problem with the ECM.
Replace the ECM. Refer to the electronic troubleshooting procedure Troubleshooting, "Replacing the ECM".
STOP
- Not OK - At least one check of the resistance does not indicate that a short circuit condition exists. There is an open circuit or excessive resistance in the harness. There may be a problem with a connector.
Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Verify that the original problem is resolved.
STOP