PISTON 1850232 - Caterpillar

System Operation Description:Use this procedure to troubleshoot suspect problems with the circuit for the electrical power supply.This procedure covers the following diagnostic codes:
168-2 Electrical System Voltage : Erratic, Intermittent, or Incorrect
336-2 Engine Control Switch : Erratic, Intermittent, or IncorrectElectrical power is supplied to the following components:
Electronic Control Module (ECM)
Optional Auxiliary Sensing Module (ASM)
Integrated Temperature Sensing Module (ITSM)
Fuel metering valve
Actuator for the throttle
Actuator for the compressor bypass groupNote: If an open circuit is suspected in the circuit between the power supply and the powered component also inspect the power distribution box for the following conditions:
Abrasion of the insulation on the wiring within the box
Damage to the posts for the wiring to the circuit breakers
Damage to the internal parts of the circuit breakersThose conditions can contribute to the following difficulties with operation:
Unstable engine performance
Interruption of communication between the engine electronic control module (ECM), the fuel metering valve, the actuator for the compressor bypass, and the throttle actuator
Intermittent loss of power to the ECM
Intermittent diagnostic codes for conditions such as engine overspeed and lack of communication between electronic components
Unexpected engine shutdownThe cause of an intermittent 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. If the power is provided by an electrical power supply, the maximum allowable AC ripple voltage is 150 mV AC peak to peak. The minimum requirement for the power supply is 22 VDC at 30 amperes. The wiring from the power supply to the ECM must provide a maximum voltage drop of 1.0 VDC.The ECM input at terminal 70 of the P1 connector ("Switched +Battery") receives battery voltage from the engine control when the control is in the START mode, in the STOP mode, or in the AUTO mode. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down after the engine has shut down.For the ASM, the input at terminal 70 of the P5 connector ("Switched +Battery") receives battery voltage from the engine control when the control is in the START mode, in the STOP mode, or in the AUTO mode. When the ASM detects battery voltage at this input, the ASM will power up.The 168-2 diagnostic code indicates that the voltage of the power supply is intermittent or low while the engine is running. If the supply voltage drops to zero and stays at zero, neither ECM will log this code. The engine will shut down.The 336-2 diagnostic code indicates that the ECM has detected a problem with the circuit for the engine control.Logged diagnostic codes provide a historical record. Before you begin this procedure, use Caterpillar Electronic Technician (ET) to print the logged codes to a file.This procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after