Complete the following checkout procedure before replacing the voltage regulator or the alternator.
- When testing alternators use accurate equipment such as a digital multimeter and an amp clamp or an equivalent. See the Tool Catalog.
- Make sure the drive belts and pulleys of the
charging system are in good condition and are adjusted properly before testing the alternator. Worn belts and pulleys or loose belts will lower the output of the alternator. - The battery must be well charged, the battery cable connections must be clean and tight, and the 2A and excitation circuits must be connected properly.
1.Press the O FF key to make sure the unit is turned Off.
2.Check the battery voltage. If the battery voltage is less than 12 volts, the battery must be charged or tested to determine if it should be replaced.
3.Check the voltage at the B+ terminal on the alternator. Battery voltage must be present. If not, check the 2A circuit.
4.Check the voltage at the VOLT SENSE terminal on the alternator. Battery voltage must be present. If not, check the SENS circuit.
5.Use the Service Test mode to place the unit in high speed cool before the engine starts. See the ?P-T Microprocessor Diagnosis Manual for information about the Service Test mode.
6.Check the voltage at the EXC terminal on the alternator. Battery voltage must be present. If not, check the EXC circuit.
7.Attach a clamp-on ammeter to the 2A wire connected to the B+ terminal on the alternator.
8.Connect a voltmeter between the B+ terminal and a chassis ground.
9.Start the unit and use the Service Test mode to place the unit in high speed cool. See the ?P-T Microprocessor Diagnosis Manual, for information about the Service Test mode.
10. Connect a jumper wire between the F2 terminal and a chassis ground. This will full field the alternator.
a.Full alternator output (the alternators rated output) indicates the alternator is good but the voltage regulator needs replacement.
b. If there is low or no output, the alternator is probably faulty. However, the following items are potential causes for not charging:
•Check the alternator brushes.
•Check the 2A circuit from the alternator to the battery.
•Properly tension the alternator belt.
•Check battery cable connections and the alternator ground. They must be clean and tight.
•The battery must be in good condition and must accept a charge.
•Check for excessive or unusual amperage draw by the unit control circuits.
