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Illustration 1 g01511893
Typical schematic for the Cat Data LinkTest Step 1. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the ECM.
Illustration 2 g01139425
ECM (1) J1/P1 connectors (2) J2/P2 connectors
Thoroughly inspect connector (1) and connector (2). Refer to Troubleshooting, "Electrical Connectors - Inspect".
Illustration 3 g01394774
P1 terminals that are associated with the Cat Data Link (P1-3) Cat Data Link − (P1-9) Cat Data Link +
Illustration 4 g01365685
Terminal locations at the service tool connector that are associated with the Cat Data Link (Terminal D) Cat Data Link + (Terminal 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 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.STOPTest Step 2. Check for a Short Circuit
Disconnect the P1 ECM connector and the P2 ECM connector.
Disconnect Cat ET from the service tool connector.
Disconnect any other control modules from the Cat Data Link. Refer to the electrical schematic in order to identify other control modules that are on the Cat Data Link.
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.
Table 1
Resistance Measurements for the Cat Data Link    
Connector and Terminal    Terminal    
P1-9 (Cat Data Link +)     All of the other terminals on the P1 connector and the P2 connector    
Ground stud
P1-3 (Cat Data Link -)     All of the other terminals on the P1 connector and the P2 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.STOPTest Step 3. Check for an Open Circuit
Fabricate a jumper wire. Use the jumper wire in order to create a short circuit between terminals D (Cat Data Link +) and terminal E (Cat Data Link −) on the service tool connector.
Measure the resistance between P1-9 (Cat Data Link +) and P1-3 (Cat Data Link −).
Measure the resistance between the terminals at the connector for each control module that was connected to the Cat Data Link. Refer to Illustration 1.
Remove the jumper wire from the service tool connector.Expected Result:Each check of the resistance indicates a short circuit.Results:
OK - Each check of the resistance indicates a short circuit.Repair: Perform the following procedure:
Connect the ECM 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. Refer to Troubleshooting, "ECM - Replace".STOP
Not OK - At least one check of the resistance does not indicate a short 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