COUPLING AS- 4809478 - Caterpillar

Note: This procedure checks for an open circuit or 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 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.
Illustration 1 g01141420
Schematic diagram of the Cat Data Link
Test Step 1. Inspect the Electrical Connectors and the Wiring
Turn the keyswitch to the OFF position.
Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the connectors to other modules on the Cat Data Link. Refer to Troubleshooting, "Electrical Connectors - Inspect".
Illustration 2 g01104274
P1 terminals that are associated with the Cat Data Link
(P1-8) Cat Data Link +
(P1-9) 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 the ECM connectors for the proper torque. 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 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.
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.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 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