HEAD 9T1851 - Caterpillar

This diagnostic code is recorded when the PL522 and 523 detects a battery voltage of less than 11 VDC.Test Step 1. CHECK THE SYSTEM VOLTAGE AT THE 70-PIN CONNECTOR OF THE PL522 AND 523 MODULE.Start the engine and operate the engine at a high idle for 5 to 10 minutes. Measure the system voltage between the "Unswitched Power" and the "Ground" contacts. Pin 52 is the terminal for "Unswitched Power" and pin 65 is the terminal for "Ground".Expected Result:The voltage is 27 VDC to 29 VDC for a 24 VDC system. The voltage is 13 VDC to 15 VDC for a 12 VDC system.Results:
OK - The voltage is correct. Clear the diagnostic code and check for another occurrence of the diagnostic code.STOP
NOT OK - The voltage is incorrect. Proceed to Test Step 2.Test Step 2. CHECK THE ALTERNATOR.Run the engine at a high idle for 5 to 10 minutes. Measure the voltage output at the battery posts.Expected Result:For a 24 VDC system, the voltage range should be 27 VDC to 29 VDC. The voltage range should be 13 VDC to 15 VDC for a 12 VDC system.Results:
OK - The voltage is correct. Proceed to Test Step 3.
NOT OK - The voltage is incorrect.Repair: Repair the alternator or replace the alternator.STOPTest Step 3. CHECK THE BATTERY VOLTAGE.Turn the keyswitch to the OFF position. Measure the battery voltage at the battery posts. Be sure to use proper Personal Protective Equipment.Expected Result:The voltage should be 12 VDC to 15 VDC for a 12 VDC system. The voltage should be 24 VDC to 27 VDC for a 24 VDC system.Results:
OK - The voltage is between 12 VDC and 15 VDC or the voltage is between 24 VDC and 27 VDC.Repair: The PL522 or 523 could be faulty. Recheck the system before replacing the PL522 or 523. The PL522 or 523 is seldom the cause of a diagnostic code. Refer to Systems Operation, Troubleshooting, Testing and Adjusting, "Electronic Control Module (ECM) - Replace". If the PL522 or 523 has been replaced, recheck the system and check the status of the diagnostic code.STOP
NOT OK - The voltage is not between 12 VDC and 15 VDC or the voltage is not between 24 VDC and 27 VDC.Repair: See Special Instruction, REHS0354, "Charging System Troubleshooting". If conditions are not resolved, the PL522 or 523 could be faulty. Recheck the system before replacing the PL522 or 523. The PL522 or 523 is seldom the cause of a diagnostic code. Refer to Systems Operation, Troubleshooting, Testing and Adjusting, "Electronic Control Module (ECM) - Replace". If the PL522 or 523 has been replaced, recheck the system and check the status of the diagnostic code.STOP