SEAL AS 9X4586 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit for electrical power supply. Also, use this procedure if one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table
CDL Code and Description Conditions which Generate this Code System Response
168-2 Electrical System Voltage : Erratic, Intermittent, or Incorrect The Electronic Control Module (ECM) has detected a supply voltage of less than 6 V while the engine is running. The code is logged.
The alarm output is activated.
336-2 Engine Control Switch : Erratic, Intermittent, or Incorrect The ECM has detected a combination of inputs for the engine control switch that is invalid. The code is logged.
The alarm output is activated.
The shutdown output is activated.
The engine is shut down. Electrical power from the batteries is supplied to the following components:
Master Electronic Control Module (ECM)
Slave ECM (20 cylinder engines only)
Fuel metering valve
Throttle actuator
Compressor bypass actuator
Control panel for the Advisor moduleThe cause of an intermittent problem with the power supply can occur on either the positive side or the negative side of the power supply.The 24 VDC power supply for the engine can be provided by a battery or by an electrical power supply. The minimum requirement for the power supply is 22 VDC at 16 A.The components are electrically protected by three fuses that are located in the junction box. The junction box is mounted to the left side of the engine.Both the master ECM and the slave ECM receive keyswitch power from the engine control switch. Terminal location P1-70 and P3-70 are used for this purpose. Keyswitch power is available at this terminal when the engine control switch is in the START position, the STOP position, or the AUTO position. When the master ECM and slave ECM detects battery voltage at the keyswitch input, the control modules will power up. When battery voltage is removed from this input, the control modules will power down.Note: If replacement of the engine control switch is necessary, be sure to use replacement parts that have been approved by Caterpillar. The use of aftermarket parts may cause adverse conditions during engine starting and/or engine operation.The fuel metering valve, the actuator for the bypass valve, and the throttle actuator receive electrical power via dedicated fuses at the junction box.A digital return at terminal location P1-31 is used as a ground source by the engine control switch. The position of the switch is reported to the master ECM via terminal locations P1-61, P1-62, and P1-64. The engine control switch provides a ground path to the appropriate terminal location as the position of the engine control switch is changed. The ECM input circuitry monitors the position of the engine control switch by detecting the ground source at these terminal locations. This information is used by the ECM for the engine state control.A problem with the electrical power supply is probably caused by a problem with the batteries. The next likely cause is a problem in the