0323783 JOHNSON SCREW, Plug

Table 1
Diagnostic Codes    
J1939 Code    Description    
158-2     Battery Potential (Voltage) Switched : Erratic, Intermittent, or Incorrect    
168-2     Electrical Potential (Voltage) : Erratic, Intermittent, or Incorrect    
168-3     Electrical Potential (Voltage) : Voltage Above Normal    
168-4     Electrical Potential (Voltage) : Voltage Below Normal    The Electronic Service Tool Will Not Communicate with the ECM - If either unswitched battery voltage or switched battery voltage is missing from the P1 connector, the Caterpillar Electronic Technician (ET) will not communicate with the ECM. The ECM requires the keyswitch to be in the ON position in order to communicate. Usually, the data link connector receives unswitched battery voltage. An indicator on the communications adapter indicates when the communications adapter is receiving battery voltage.158-2 (J1939) - The voltage on the keyswitch input transitions from a low voltage to a high voltage at least three times in one second. A snapshot is triggered.168-2 (J1939) - The engine is running. The battery voltage at the P1 terminals has fallen below 6 VDC for at least 0.5 seconds. The ECM may stop injecting fuel. This depends on the length of time of the occurrence of the problem. The check engine lamp and the warning lamp may come on. The engine may experience changes in engine rpm. Intermittent engine shutdowns or complete engine shutdowns may occur.168-3 (J1939) - The engine is running. The battery voltage at the P1 terminals is above 16 VDC for at least 0.5 seconds. A snapshot is triggered.168-4 (J1939) - The engine is running. The battery voltage at the P1 terminals has fallen below 9 VDC for at least three seconds. A snapshot is triggered and the engine is derated. The low voltage condition can be caused by a problem on either the positive side or on the negative side of the battery circuit. The following components can cause these codes:
Electrical connector or wiring
Keyswitch
ECMThe most likely cause of the code is a problem with an electrical connector or with the wiring. The least likely cause is a problem with the ECM.Power CircuitThe ECM receives battery voltage through wiring that is supplied by the vehicle manufacturer. Unswitched battery voltage is supplied to three terminals on the ECM P1 connector. The negative battery is also supplied to three terminals on the P1 connector.Keyswitch CircuitThe ECM receives battery voltage from the keyswitch on terminal P1-70 when the keyswitch is in the ON position or in the START position. When the ECM detects battery voltage on this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down. Engine Shutdown SystemsSome vehicles may be equipped with an engine protection shutdown system or an idle timer shutdown system that interrupts electrical power to the keyswitch. The engine protection shutdown system can be an aftermarket device and the idle timer shutdown system can be external to the ECM. Some of these systems will not supply power to the ECM until one of the following conditions is met:
The engine is cranked.
The engine oil pressure achieves acceptable limits.
An override button is pressed.Keep in mind that these devices may be the cause of intermittent power to the ECM. These devices may also shut down the engine.Diagnostics on Cat ETCat ET provides the following diagnostics:Wiggle Test - The wiggle test allows you to monitor the "ECM Battery Voltage" parameter and the "Ignition Key Switch" parameter while you wiggle the wiring. This helps to identify faulty electrical connections.Snapshots - When these diagnostic codes occur, the ECM records the status of the "ECM Battery Voltage" parameter and the "Ignition Key Switch" parameter for 9.6 seconds before the diagnostic code and 3.4 seconds after the diagnostic code.For additional information regarding the use of these diagnostics, refer to the documentation that accompanies your Cat ET software.
Illustration 1 g03020381
Test Step 1. Determine the ProblemIf Cat ET will not communicate with the ECM, refer to the appropriate result for this Test Step.If Cat ET will communicate with the ECM, use Cat ET to determine the diagnostic code.Do not troubleshoot a logged code unless the code relates to an engine symptom. If the code is logged and the code does not relate to an engine symptom, clear the code.Results:
No Communication - Proceed to Test Step 2.
Active or logged 168-3 (J1939) code - Repair: The most likely cause of the code is a problem with the charging system. Refer to Systems Operation/Testing and Adjusting, "Charging System - Test".If the charging system is working correctly and the code is still active, replace the ECM. Refer to Troubleshooting, "ECM - Replace".STOP
Logged 168-4 (J1939) or 168-2 (J1939)code - Proceed to Test Step 4.
Logged 158-2 (J1939) code - Proceed to Test Step 5.
Active 168-4 (J1939) or 168-2 (J1939) code - Proceed to Test Step 6.
Active 158-2 (J1939) code - Proceed to Test Step 8.Test Step 2. Check the Voltage at the P1 Connector
Measure the voltage at the battery terminals.The battery voltage must be above 11 VDC in order to continue with this procedure.
Verify that the keyswitch is in the ON position.
Use 7X-1710 Multimeter Probes to measure the voltage between the following terminals:
P1-53 (Unswitched +Battery) and P1-65 (-Battery)
P1-70 (Keyswitch) and P1-65 (-Battery)Both voltage readings should be within two volts of the battery voltage.Expected Result:At least one of the voltage readings is less than nine VDC.Results:
Yes - At least one of the voltage readings is less than nine VDC.Repair: Perform the following procedure:
Verify that there are no aftermarket devices that are preventing battery voltage from reaching the ECM. Some type of override switch is interrupting the power to the ECM if the following conditions are true:
Communication occurs when the engine is running.
No communication occurs when the engine is not running and the keyswitch is ON.
Disable the aftermarket device, if necessary.
Measure the voltages again. If either voltage measurement is below nine VDC, there is a problem with the wiring between the P1 connector and the battery.The wiring between the P1 connector and the battery is provided by the Original Equipment Manufacturer (OEM).