Note: This procedure checks for an open circuit or for a short circuit in the Cat Data Link. Use this test if you are experiencing problems with communications between the Electronic Control Module (ECM), the machine control module, electronic transmission controls, electronic dash displays, and Caterpillar Electronic Technician (ET). If you are experiencing problems with communications for Cat ET, refer to 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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| Illustration 1 | g01181789 |
Schematic for the Cat Data Link | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the J1/P1 ECM connectors. Also, thoroughly inspect each connector that is in the circuit for the Cat Data Link. Refer to Troubleshooting, "Electrical Connectors - Inspect".
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| Illustration 2 | g01183529 |
Location of the P1 ECM connector (typical left side engine view) | |
- 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 3 | g01104274 |
P1 terminals that are associated with the Cat Data Link (P1-8) Cat Data Link + (P1-9) 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 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.
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 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. 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. Use the jumper wire in order to create a short circuit between terminals J63-D (Cat Data Link +) and J63-E (Cat Data Link −).
- Measure the resistance between P1-8 (Cat Data Link +) and P1-9 (Cat Data Link −).
Expected Result:
Each check of the resistance is less than ten Ohms.
Results:
- OK - Each check of the resistance is less than ten Ohms.
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 check of the resistance is greater than ten Ohms. 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