Low Voltage Disconnect, Sure Power 54.18

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Clarence Atkins
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1 Low Voltage Disconnect, Sure Power Functional Test NOTE: If the LVD deactivates (removes power to the cab/sleeper loads), it needs to be reset prior to performing a functional test. If the batteries are discharged below 12.3 volts, charge the batteries before performing any troubleshooting procedures. The LVD can be reset by starting the engine. Once the LVD senses 13.1 volts or more, it resets automatically. 1. Shut down the engine. 2. Unplug the 10-position connector from the LVD. 3. Remove wire 447B from cavity E on the connector, and wrap a small piece of electrical tape around the exposed wire. 4. Insert the plug into the LVD with wire 447B still removed. NOTE: The red LED indicator light on the LVD should turn ON when the connector is inserted. 5. Insert a metal conducting probe into cavity E of the connector, making sure contact is made between the metal probe and pin E on the LVD. 6. Connect a jumper wire between the terminal on wire 447B and the test probe inserted in cavity E. NOTE: The electrical loads such as dome lights will remain OFF even though an electrical connection exists between circuit 447B and pin E. The LVD needs to be reset after removing the plug from the LVD. 7. Reset the LVD by starting the engine. The dome lights should come back ON, and the red LED indicator light on the LVD should turn OFF. 8. Shut down the engine. 9. Remove the metal test probe from cavity E. NOTE: After removing the test probe, there will be a delay before the LVD disconnects the cab/ sleeper loads. If equipped with the optional warning buzzer, it will sound for 60 seconds. After the time delay, the cab/sleeper loads (dome lights, for example) will shut OFF, and the optional warning buzzer will shut OFF. 10. Disconnect the jumper wire from 447B. 11. Remove the 10-position connector from the LVD. 12. Insert wire 447B into cavity E of the connector. 13. Insert the connector into the LVD. 14. Start the engine to reset the LVD. 15. If the LVD does t operate properly after performing the functional test, perform the troubleshooting procedures in this subject. Table Low Voltage Disconnect System Refer to Table 1 to troubleshoot the low voltage disconnect system. Low Voltage Disconnect System Malfunctions Problem Battery voltage goes below 12.1 (minal) volts without low voltage disconnect system activation. Low voltage disconnect system always activated. The low voltage disconnect system activates without the warning buzzer sounding. The warning buzzer activates without low voltage disconnect system activation. Table 1, Low Voltage Disconnect System Malfunctions Remedy Check the low voltage disconnect module and associated wiring. See Fig. 1. Check the low voltage disconnect module and associated wiring. See Fig. 2. Check the warning buzzer and wires 14BS and 447J. See Fig. 3. Check the warning buzzer and wire 447J. See Fig. 4. Century Class Trucks Workshop Manual, Supplement 29, June /1

2 54.18 Low Voltage Disconnect, Sure Power Are the batteries fully charged (12.6 volts)? Charge the batteries, and start the engine. Battery voltage must be above 13.1 volts to reset the system. Is the LED indicator on the low voltage disconnect module illuminated? The module is working properly. Is battery voltage present at the V sense terminal of the low voltage disconnect module? Check the V sense fuse in the battery box. If the fuse is OK, check the 447B wiring between the low voltage disconnect module and the battery for an open or a short to ground. Is continuity to ground present at ground terminal of the low voltage disconnect module? Check the low voltage disconnect ground fuse in the battery box. If the fuse is OK, check the GND wiring between the low voltage disconnect module and the battery for an open. Is battery voltage present at the V in terminal of the low voltage disconnect module? Check the 14B wiring between the low voltage disconnect module and the firewall power stud for an open or a short to ground. 11/21/97 f Fig. 1, Battery Voltage Goes Below 12.1 Volts Without Low Voltage Disconnect System Activation 300/2 Century Class Trucks Workshop Manual, Supplement 29, June 2008

3 Low Voltage Disconnect, Sure Power Are the batteries fully charged (12.6 volts)? Charge the batteries, and start the engine. Battery voltage must be above 13.1 volts to reset the system. Is the LED indicator on the low voltage disconnect module illuminated? Is battery voltage present at the V out terminal of the low voltage disconnect module? Is the 14BS wiring between the low voltage disconnect module and the ISO terminal on the power distribution module shorted to ground? Check the 14BS wiring between the low voltage disconnect module and the ISO terminal of the power distribution module for an open. Repair or replace the 14BS wire. Is battery voltage present at the V sense terminal of the low voltage disconnect module? Check the V sense fuse in the battery box. If the fuse is OK, check the 447B wiring between the low voltage disconnect module and the battery for an open or a short to ground. Is continuity to ground present at ground terminal of the low voltage disconnect module? Check the low voltage disconnect ground fuse in the battery box. If the fuse is OK, check the GND wiring between the low voltage disconnect module and the battery for an open. Is battery voltage present at the V in terminal of the low voltage disconnect module? Check the 14B wiring between the low voltage disconnect module and the firewall power stud for an open or a short to ground. 11/21/97 f Fig. 2, Low Voltage Disconnect System Always Activated Century Class Trucks Workshop Manual, Supplement 29, June /3

4 54.18 Low Voltage Disconnect, Sure Power Is the LED indicator on the low voltage disconnect module on? Charge the batteries, and start the engine. Battery voltage must be above 13.1 volts to reset the system. Is battery voltage present at wire 14BS at pin 1 of the warning buzzer? Check wire 14BS for an open between pin 1 of the warning buzzer and the V out terminal of the low voltage disconnect module. Disconnect wire 447J from the warning buzzer control terminal of the low voltage disconnect module and connect wire 447J to a good ground. Does the warning buzzer sound? Check wire 447J for an open. If wire 447J is OK, replace the warning buzzer. 11/21/97 f NOTE: Under rmal circumstances, the warning buzzer only sounds for 1 minute after low voltage disconnect module LED activation. Fig. 3, The Low Voltage Disconnect System Activates Without the Warning Buzzer Sounding 300/4 Century Class Trucks Workshop Manual, Supplement 29, June 2008

5 Low Voltage Disconnect, Sure Power Is the LED indicator on the low voltage disconnect module on? Fully charge the batteries. Is the warning buzzer sounding? The low voltage disconnect module is working properly. Disconnect wire 447J from the warning buzzer control terminal of the low voltage disconnect module. Is the warning buzzer sounding? Check wire 447J for a short to ground. If wire 447J is OK, replace the warning buzzer. 08/07/97 f Fig. 4, The Warning Buzzer Activates Without Low Voltage Disconnect System Activation Century Class Trucks Workshop Manual, Supplement 29, June /5

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