0340842 JOHNSON SENSOR SUPPORT

Table 1
Diagnostic Codes Table    
Diagnostic Codes Table     Conditions which Generate this Code     System Response    
248-9 Cat Data Link not communicating     The engine Electronic Control Module (ECM) is not receiving complete information.     The code is logged.
If equipped, the warning light will illuminate.
All features that rely on the data link are disabled.    
1639-2 Machine Security System Module erratic, intermittent, or incorrect     The serial number of the Machine Security System (MSS) that is stored in the ECM does not match the serial number of the MSS.     The code is logged.
If equipped, the warning light will illuminate.
The engine will not start until the correct serial number is entered.    
1639-9 Machine Security System Module abnormal update rate     The engine ECM detects a loss of communications with the MSS.     The code is logged.
If equipped, the warning light will illuminate.
The engine will not start.    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 electronic service tool and the ECM, refer to service 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 the electronic service tool. The ECM communicates with the electronic service tool in order to share status information and diagnostic information. The electronic service tool can also be used to configure the ECM parameters. This information will not be available if communication fails between the ECM and the electronic service tool.If the diagnostic connector is on the engine, the positive data link signal will be from P2-21 to pin "D" of the diagnostic connector. The negative data link signal will be from P2-20 to pin "E" of the diagnostic connector.If the diagnostic connector is off the engine, the positive data link signal will be from P1-23 to pin "D" of the diagnostic connector. The negative data link signal will be from P1-24 to pin "E" of the diagnostic connector.
Illustration 1 g01325018
Schematic of the diagnostic connector and the ECM
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 g01325019
A typical view of the P1 connector (harness side) pin locations. (23) Cat data link (CDL) + (24) Cat data link (CDL) -Test Step 1. Inspect the Electrical Connectors and the Wiring
Remove the electrical power from the ECM.
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. Refer to service Troubleshooting, "Electrical Connectors - Inspect".Expected Result:All connectors, pins, and sockets are correctly 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 correctly coupled.If applicable, use the electronic service tool to perform the "Wiggle Test" on the wires that are associated with the Cat Data Link.Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.STOPTest Step 2. Check for a Short Circuit
Disconnect the electronic service tool 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 2. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
Table 2
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.Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.STOPTest Step 3. Check for an Open Circuit
Fabricate a jumper wire. Use the jumper wire to create a short circuit between terminals D (Cat Data Link +) and terminal E (Cat Data Link -) on the diagnostic connector.
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 the electronic service tool to the diagnostic 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