The CAT Data Link is a two wire electrical connection that is used for communication between electronic modules such as the engine Electronic Control Module (ECM), the machine electronic control module, electronic transmission controls, electronic dash displays, and the Caterpillar Electronic Technician (Cat ET).
The ECM communicates with display modules in order to share engine information and diagnostics for the electronic system.
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 | g00898543 |
Schematic | |
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| Illustration 2 | g00898659 |
P1 ECM connector | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Turn the keyswitch to the OFF/RESET position.
- Thoroughly inspect the J1/P1 ECM connector and the J3/P3 machine connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Note: Refer to the Electrical System Schematic for further information about the machine wiring.
Expected Result:
All connectors, pins, and sockets should be completely inserted and coupled. The harness and wiring should be free of corrosion, abrasion, and pinch points.
Results:
- OK - Proceed to Test Step 2.
- Not OK -
Repair: Repair the circuit.Verify that the repair eliminates the problem.
Stop.
Test Step 2. Check for Shorts in the Harness
- Disconnect the J1/P1 ECM connector.
- Disconnect all modules from the CAT Data Link.
- Disconnect Cat ET from the service tool connector.
- Measure the resistance between P1:3 (CAT Data Link -) and P1:9 (Cat Data Link +).
- Measure the resistance between P1:9 (Cat Data Link +) and chassis ground.
- Measure the resistance between P1:3 (CAT Data Link -) and chassis ground.
Expected Result:
The resistance should be greater than 20,000 Ohms for each measurement.
Results:
- OK - Proceed to Test Step 3.
- Not OK - There is a short circuit in the harness or connectors.
Repair: Repair the circuit.Verify that the repair eliminates the problem.
Stop.
Test Step 3. Check the Resistance Through the Harness
- Use a suitable piece of wire to short J42:D (CAT Data Link +) and J42:E (CAT Data Link -) at the service tool connector.
- Measure the resistance between P1:9 (CAT Data Link +) and P1:3 (CAT Data Link -).
- Measure the resistance across the CAT Data Link at the other modules.
Expected Result:
The resistance should be less than 10 Ohms for each measurement.
Results:
- OK - The CAT Data Link is OK.
Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.
Stop.
- Not OK - There is an open circuit or excessive resistance in the harness or connectors.
Repair: Repair the circuit.Verify that the repair eliminates the problem.
Stop.