COUPLING 7C1822 - Caterpillar

Note: This procedure checks for an open circuit or for 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 Does Not Communicate" 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 g01368914
Schematic for the Cat Data Link
Illustration 2 g06112342
Connector location for the Cat Data Link (typical left side rear engine view)
(1) Engine interface connector (70 pin)
(2) Service tool connector
(3) J1/P1 ECM connector
Illustration 3 g01312112
Terminal locations at the P1 ECM connector that are associated with the Cat Data Link
(P1-8) Cat Data Link +
(P1-9) Cat Data Link −
Illustration 4 g01367380
Terminal locations at the P1 ECM connector that are associated with the Cat Data Link
(P1-8) Cat Data Link +
(P1-9) Cat Data Link −
Illustration 5 g01365685
Terminal locations at the P1 ECM connector that are associated with the Cat Data Link
(P1-8) Cat Data Link +
(P1-9) Cat Data Link −
Table 1
Troubleshooting Test Steps Expected Results Results
1. Inspect the Electrical Connectors and the Wiring
A. Remove electrical power from the ECM.
B. Thoroughly inspect connectors (1), (2), and (3). Refer to Troubleshooting, "Electrical Connectors - Inspect".
C. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the Cat Data Link.
D. 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.
All connectors, pins, and sockets are inserted and coupled completely. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Result: The harness and the connectors appear to be OK. Proceed to Test Step 2
Result: The connectors and/or the wiring are not OK.
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 coupled completely. Verify that the original problem is resolved.
Table 2
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
Negative ground
P1-9 (Cat Data Link -) All of the other terminals on the P1 connector
Negative ground
Table 3
Troubleshooting Test Steps Expected Results Results
2. Check for a Short Circuit
A. Disconnect the P1 ECM connector.
B. Disconnect Cat ET from the service tool connector.
C. Measure the resistance between the points that are listed in Table 2. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
Each check of the resistance indicates an open circuit.
Result: Each check of the resistance indicates an open circuit. Proceed to Test Step 3.
Result: At least one check of