CP54B, CP56B, CP68B, CP74B, CS54B, CS56B, CS64B, CS66B, CS68B, CS74B, CS76B and CS78B Vibratory Soil Compactors Machine Electronic Control System Caterpillar

Electrical Power Supply - Test

Usage:

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.

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Illustration 1	g03865626
Machine ECM Power Supply 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.

For the full Electrical Schematic of the Soil Compactors in this manual, refer to the appropriate media listed below.

For models CS54B and CP54B refer to Electrical Schematic, UENR6386.
For models CS56B, CP56B, CS64B, CS66B, CS68B and CP68B refer to Electrical Schematic, UENR6388.
For models CS74B, CP74B, CS76B and CS78B refer to Electrical Schematic, UENR6384.

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.

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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 J1 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 times. Proceed to Test Step 2.
2. Check The Ground Circuits A. Turn the key start switch and the disconnect switch OFF. B. Disconnect the harness connector from the ECM. C. At the harness connector for the ECM, measure the resistance between each of the negative battery contacts and frame ground. The contacts for the negative battery connections are illustrated in the diagram at the beginning of this procedure.	Each resistance is less than 5.0 Ω.	OK - Each resistance is less than 5.0 Ω. Proceed to Test Step 3. NOT OK - A resistance is greater than 5k Ω. There is an open circuit or a poor connection in the ground circuit. Repair: Check all of the connectors and splice points that are in the ground circuit. Ensure that all connections are clean, secure, and in good condition. Repair or replace the machine harness. Proceed to Test Step 6.
3. Check The Supply Circuits A. The key start switch and disconnect switch remain OFF. The ECM harness connector remains disconnected. B. At the harness connector for the ECM, using a length of wire, measure the resistance between the alternator "B" terminal and each of the positive battery contacts that are connected to the harness connector. The contacts for the five positive battery connections are illustrated in the diagram at the beginning of this procedure.	Each resistance is less than 5.0 Ω.	OK - Each resistance is less than 5.0 Ω. Proceed to Test Step 6. NOT OK - A resistance is greater than 5k Ω. There is an open circuit or a poor connection in the supply circuit. Repair: The open or poor connection is in the ground circuit. Check all of the connectors and splice points that are in the ground circuit. Ensure that all connections are clean, secure, and in good condition. Repair or replace the machine harness. Proceed to Test Step 6.
4. Check The Alternator Current Output A. Reconnect the ECM harness connectors. B. Partially discharge the batteries by cranking the engine for 30 seconds or turning on the lights for about 10 minutes without starting the engine. C. Turn the disconnect switch and the key start switch OFF. D. Connect multimeter probes between the alternator "B" terminal and the alternator case. E. Connect a clamp-on 225-8266 Ammeter Tool Gp or an equivalent ammeter around the output wire. F. Turn the disconnect switch ON. G. Start the engine and run the engine at approximately half throttle. H. Immediately check the alternator output current.	The alternator output current at half throttle is approximately half the alternator full current output rating, and is stable.	OK - The alternator output current at half throttle is approximately half the alternator full current output rating, and is stable. Proceed to Test Step 5. NOT OK - The output current of the alternator at half throttle is not stable. There is a large variation in the currents. Repair: Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures. Proceed to Test Step 6.
5. Check The Alternator Voltage Output A. The multimeter and the ammeter are still connected. B. Run the engine for approximately 10 minutes at half throttle. C. Check the alternator voltage at terminal "B".	The voltage is within range of system voltage. There is little or no variation in the voltage. 28 ± 1 V for 24 V system.	OK - The voltage is within range of system voltage and is stable. Proceed to Test Step 6. NOT OK - The voltage is not stable. There is a large voltage variation. Repair: Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures. Proceed to Test Step 6.
6. Check If The Failure Remains A. Reconnect all harness connectors. Return machine to normal operating condition. B. Turn the key start switch and the disconnect switch ON. C. Clear all diagnostic codes. D. Operate the machine. E. Stop the machine and engage the safety lock. F. Check if the failure still exists.	The failure is no longer present.	OK - The failure does not exist at this time. The failure may have been caused by poor electrical connection or short at one of the harness connections. Resume machine operation. STOP. NOT OK - The failure has not been corrected. If the failure has not been corrected after performing the procedure a second time, the ECM may require replacement. Prior to replacing the ECM, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may effect repair time. Follow the steps in Troubleshooting, "ECM - Replace" if the ECM needs to be replaced. STOP.