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Illustration 1 g01208091
Schematic diagram of the Cat Data LinkTest Step 1. Inspect the Electrical Connectors and the Wiring
Remove the electrical power from the ECM.
Thoroughly inspect the connectors for each of the modules. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".
Illustration 2 g01210023
Engine ECM P1 terminals that are associated with the Cat Data Link (P1-8) Cat Data Link + (P1-9) Cat Data Link −
Illustration 3 g01210026
Machine ECM P1 terminals that are associated with the Cat Data Link (P1-7) Cat Data Link − (P1-8) 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 torque of the allen head screws for the ECM connectors. 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.STOPTest Step 2. Check for a Short Circuit
Verify that the electrical power is removed from the ECM.
Disconnect Cat ET from the service tool connector.
Measure the resistance between the points that are listed in Table 1. You may perform the measurements at either service tool connector. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
Table 1
Service Tool Connector
Resistance Measurements for the Cat Data Link    
Terminal    Terminal    
D (Cat Data Link +)     E (Cat Data Link -)    
A (+Battery)
B (-Battery)
E (Cat Data Link -)     A (+Battery)    
    B (-Battery)    Expected Result:Each check of the resistance is greater than ten Ohms.Results:
OK - Each check of the resistance is greater than ten Ohms. Proceed to Test Step 3.
Not OK - At least one check of the resistance is less than ten Ohms. There is a short circuit in a harness. There may be a problem 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 E (Cat Data Link −) on a service tool connector.
Refer to the electrical schematic. Disconnect the appropriate connector from the suspect module.
Measure the resistance between the terminals for the Cat Data Link on the connector for the suspect module. Be sure to wiggle the wires in the harnesses as you measure the resistance.Expected Result:The resistance is less than ten Ohms.Results:
OK - The resistance is less than ten Ohms. The wiring between the service tool connector and the connector for the suspect module does not have an open circuit. Proceed to Test Step 4.
Not OK - The resistance measurement 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.STOPTest Step 4. Check the ModulesTemporarily install a new module in place of the suspect module. Check for the diagnostic code again.Expected Result:The diagnostic code is not active when the suspect module is replaced.Results:
OK - The diagnostic code is not active when the suspect module is replaced.Repair: If the problem is resolved with a new module, install the original module and verify that the problem returns. If the new module works correctly and the original module does not work correctly, replace the original module.STOP
Not OK - The diagnostic code remains active when the suspect module is replaced.Repair: Install the original module. Then, temporarily install another module. After you temporarily install each module, check for the code again. When the diagnostic code is no longer active, the faulty module has been identified. Replace the faulty module.STOP