HEAD 8J9435 - Caterpillar

Machine ECM
There is no Diagnostic Trouble Code associated with the electrical power supply for the ECM.The electrical power supply connections are the connections between the alternator and battery that power the control modules.Possible causes for an Electrical System Power Supply failure:
A poor connection in the ground circuit.
A poor connection in the voltage supply circuit.
The alternator or charging system has failed.
The alternator is producing too much voltage.
The circuit in the machine harness is shorted to ground.
The ECM has failed. A failure of the ECM is unlikely.
Illustration 1 g03872825
Power Supply Machine ECM connections
The diagram above is a simplified schematic of the System Voltage Machine ECM connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown.See the entire electrical system schematic of the machine for more information. The entire schematic illustrates every component and the wire connections. All of the wiring harnesses that are important to troubleshooting and repair are illustrated on the system schematic. The part number of the components is listed in addition to the number for the harnesses.For the full Electrical Schematic of the Pneumatic Compactors in this manual, refer to the appropriate media listed below.
For Machine models (S/N: B7L), refer to Electrical Schematic, UENR2688.
For Machine models (S/N: AL3), refer to Electrical Schematic, UENR2417.Diagnostic Trouble Code Procedure
Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure, and in good condition. Ensure that the Charging System is functioning properly. Check the wiring harness for pinch points or abrasions. Look for and repair areas that indicate wires are exposed. If a problem with a connection is found, correct the problem and verify that the diagnostic code is active before performing a troubleshooting procedure.
Table 1
Troubleshooting
Troubleshooting Test Steps Values Results
1. Check System Voltage At The ECM
A. Turn the disconnect switch and the key start switch OFF.
B. At the harness connector for the ECM, insert a 7X-1710 Multimeter Probe along the power supply. Use the other multimeter probe to make contact to frame ground.
C. Turn the disconnect switch ON. Start the engine and run at half throttle.
D. Measure the voltage between the power supply contact and frame ground.
E. Measure the voltage between the power supply contact and the (-) battery contact at the ECM harness connector.
Both voltages are approximately the same and are within range of the system voltage. OK - Each voltage is approximately the same and is within range of the system voltage.
Proceed to Test Step 6.
NOT OK - The voltages are approximately the same, however the voltages are unstable. There is a large variation in the voltages.
Proceed to Test Step 4.
NOT OK - The positive battery contact to frame ground measurement is stable and within range of the system voltage. However, the measurement between the ECM positive battery contact and the ECM negative battery contact is not stable in the correct range at all