Use this procedure to troubleshoot the electrical system if a problem is suspected with the Cat Data Link.
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 Troubleshooting, "Electronic Service Tool Does Not Communicate" 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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| Illustration 1 | g01415935 |
Schematic for the Cat Data Link | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove electrical power from the ECM.
- Thoroughly inspect connectors (1), (2), and (3). Refer to Troubleshooting, "Electrical Connectors - Inspect".
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| Illustration 2 | g01380568 |
Connector locations for the CAT data link (rear engine view) (1) P1 ECM connector (2) Customer connector | |
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| Illustration 3 | g01380580 |
Connector locations for the CAT data link (top rear engine view) (2) Customer connector (3) Service tool connector | |
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the Cat Data Link.
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| Illustration 4 | g01312112 |
Terminal locations at the P1 ECM connector that are associated with the Cat Data Link (P1-8) Cat Data Link + (P1-9) Cat Data Link − | |
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| Illustration 5 | g01367380 |
Terminal locations at the Customer Connector that are associated with the Cat Data Link (Terminal 6) Cat Data Link − (Terminal 7) Cat Data Link + | |
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| Illustration 6 | g01365685 |
Terminal locations at the service tool connector that are associated with the Cat Data Link (D) Cat Data Link + (E) 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 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 for a Short Circuit
- Disconnect the P1 ECM 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.
Show/hide table
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 Negative ground P1-9 (Cat 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 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 for an Open Circuit
- Fabricate a jumper wire that is long enough to create a test circuit across two terminals at the service tool connector. Use the jumper wire in order to create a short circuit between terminals D (Cat Data Link +) and E (Cat Data Link −) on the service tool connector.
- Measure the resistance between P1-8 (Cat Data Link +) and P1-9 (Cat Data Link −).
Expected Result:
Each check of the resistance indicates a short circuit.
Results:
- OK - Each check of the resistance checks indicate a short circuit.
Repair: Perform the following procedure:
- Connect the J1/P1 connectors. Connect Cat ET to the service tool connector.
- Check the Cat Data Link for proper operation. If the data link does not operate correctly, there may be a problem with the ECM.
Temporarily install a new ECM. Check the Cat Data Link again. If the new ECM solves the problem, install the original ECM and verify that the original problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Verify that the problem is resolved.
STOP
- Not OK - At least one of the resistance measurements indicates an open circuit. 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