COLLET 1635528 - Caterpillar

System Operation Description:This procedure tests whether proper voltage is being supplied to the Engine Control Module (ECM).Note: The "Vehicle Voltage Selection" parameter determines the upper limit and the lower limit for battery voltage, that is used in order to trip the diagnostic codes for battery power. The options for programming are 12 volt or 24 volt. Typically, the parameter is set at the Caterpillar manufacturer, based on the engine order. Installing a new ECM will require the "Vehicle Voltage Selection" parameter to be programmed for the appropriate system voltage. "Vehicle Voltage Selection" will be displayed beneath the 253-02 diagnostic code, until the "Vehicle Voltage Selection" is programmed.Use this procedure to troubleshoot the system when one of the following diagnostic codes is active or easily repeated:
43-2 Key Switch Fault
168-2 ECM Battery Power Intermittent
168-3 High ECU Battery Power
168-4 Low ECU Battery PowerAlso, use this procedure if you have been directed from Troubleshooting, "Electronic Service Tool Will Not Communicate with ECM" or Troubleshooting, "Engine Cranks but Will Not Start".The ECM receives electrical power (battery voltage) through the wiring that is supplied by the vehicle manufacturer. Unswitched battery voltage is supplied to terminals P1-48, P1-52, and P1-53 at the J1/P1 ECM connectors. The negative battery is supplied to terminals P1-63, P1-65, and P1-67 at the J1/P1 ECM connectors. The ECM receives the input from the keyswitch at terminal P1-70 while the keyswitch is in the ON position or the START position. When the ECM detects battery voltage at the keyswitch input, the ECM powers up. When battery voltage is removed from this input, the ECM powers down.The cause of an intermittent power supply to the ECM can occur on either the positive side or on the negative side of the battery circuit. The three connections for the unswitched +Battery must be routed through a dedicated protection device (circuit breaker).Some 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 unexpectedly shut down the engine.Usually, the vehicle will be wired so that the battery power for the service tool connector will be independent of the keyswitch. Therefore, the communications adapter may be able to power up, but the communications adapter may not be able to establish communications with the ECM. The ECM requires the keyswitch to be in the ON position in order to maintain communications. The ECM may power down a short time after connecting Caterpillar Electronic Technician (ET) if the keyswitch is in the OFF position. This is normal.For intermittent problems such as intermittent shutdowns that