0127279 JOHNSON KEY, #70

Illustration 1 g01325018
Schematic of the diagnostic connector and the Cat Data Link connector
Illustration 2 g01325021
A typical view of the P2 connector (harness side) pin locations. (20) Cat data link (CDL) - (21) Cat data link (CDL) +
Illustration 3 g01344668
A typical view of the P2 connector (ECM side) pin locations.
Illustration 4 g01325019
A typical view of the P1 connector (harness side) pin locations. (23) Cat data link (CDL) + (24) Cat data link (CDL) -
Illustration 5 g01325662
A typical view of the P1 connector (ECM side) pin locations.Test Step 1. Inspect the Electrical Connectors and the Wiring
Turn the keyswitch to the OFF position.
Illustration 6 g01325579
Typical engine ECM (1) J2 ECM connector (2) J1 ECM connector
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 service Troubleshooting, "Electrical Connectors - Inspect" for details.
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 service Troubleshooting, "Electrical Connectors - Inspect".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.If applicable, use Cat ET to perform the wiggle test on the wires that are associated with the Cat Data Link.STOPTest Step 2. Check for a Short Circuit
Disconnect the P1 and P2 ECM connectors.
Disconnect Cat ET from the service tool connector.
Disconnect any other control modules from 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    
P1-23 (Cat data link +)     All of the other terminals on the P1 connector    
Engine ground
P1-24 (Cat data link -)     All of the other terminals on the P1 connector    
Engine ground
P2-21 (Cat data link +)     All of the other terminals on the P2 connector    
Engine ground
P2-20 (Cat data link -)     All of the other terminals on the P2 connector    
Engine ground 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 connectors.
Measure the resistance between P1-23 (Cat Data Link +) and P1-24 (Cat Data Link −).
Measure the resistance between P2-21 (Cat Data Link +) and P2-20 (Cat Data Link −).
Measure the resistance between the terminals at the connector for each control module that was connected to the Cat Data Link.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 J1/P1 and J2/P2 connectors. Connect Cat ET to the service tool connectors.
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 does not indicate a short