PIN AS 1R6224 - Caterpillar

System Operation Description:The following diagnostic codes indicate a problem with the power supply to the Electronic Control Module (ECM):
168-02 ECM Battery Power Intermittent
43-02 Key Switch FaultNote: This code can be generated by rapidly cycling the key switch. Some control modules on the vehicle require this action in order to prompt flash codes. If this occurs, clear the logged diagnostic codes in order to prevent future confusion or an incorrect diagnosis.The following background information is related to this procedure:The ECM receives electrical power (battery voltage) through the wiring that is supplied by the vehicle manufacturer. The ECM input at connector P1:70 (Ignition Key Switch) receives battery voltage from the key switch when the key switch is in the ON position or in the START position. 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.The cause of an intermittent power supply to the ECM can occur on either the positive side ("Unswitched +Battery") or the negative side ("−Battery"). Both sides are routed from the ECM to the battery. The two Unswitched +Battery connections must be routed through a dedicated protection circuit.Some vehicles may be equipped with an engine protection shutdown system or an idle timer shutdown system that interrupts electrical power to the ECM in order to shut down the engine. Also, some vehicles may be equipped with a system that interrupts electrical power to the key switch. 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.Usually, battery power to the data link connector is available and this battery power is independent of the key switch. Therefore, you will be able to power up the Caterpillar Electronic Technician (Cat ET), but you may not be able to communicate with the engine ECM. The engine ECM requires the key switch to be in the ON position in order to maintain communications. The ECM may power down a short time after connecting to Cat ET if the key switch is in the OFF position. This is normal.For intermittent problems such as intermittent shutdowns that could be caused by vehicle wiring, temporarily bypassing the vehicle wiring may be an effective means of determining the root cause. If the symptoms disappear with the bypass wiring, the vehicle wiring is the cause of the problem. This is especially important for vehicles that do not provide dedicated circuits for the unswitched battery and the key switch.
Illustration 1 g00779064
Schematic for ECM battery circuit
Illustration 2 g00640974
Terminal locations for ECMTest Step 1. Inspect Electrical Connectors and Wiring
Thoroughly inspect the J1/P1 ECM connector, the battery connections and the connections to the key switch. Refer