Testing

Open Circuit Voltage Test

1. Make sure the engine is OFF, and turn on the headlights for 15 - 20 seconds to remove any surface charge from the battery.
2. Use a DVOM (Digital Volt/Ohm Meter) set to DC volts and probe across the battery terminals.
3. Measure the battery voltage.
4. Write down the voltage reading and proceed to the next test.

No-Load Test

1. Connect a tachometer to the engine.

   CAUTION
   Place the transmission in P (Park), set the emergency brake and chock the rear wheels to prevent vehicle movement.

2. Turn off all electrical loads (radio, blower motor, wipers, etc.).

   NOTE: It is a good practice to turn off all electrical accessories prior to shutting off the engine.

3. Start the engine and increase engine speed to 1500 RPM.
4. Measure the voltage reading at the battery with the engine holding a steady 1500 RPM.
5. Voltage should increase at least 0.5 volts (no more than 2.5 volts)
6. If the voltage does not go up more than 0.5 volts, the charging system is not charging.
7. If the voltage goes up more than 2.5 volts, the alternator is overcharging.

   NOTE: Under and overcharging is typically caused by a defective alternator, or its related parts (regulator). Note that the voltage regulator is internal to the alternator assembly in many vehicles. Replacement of these items will often repair the problem. However, faulty wiring and other problems can also cause the charging system to malfunction. Further testing, which is not covered by this book, will reveal the exact component failure. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.

8. If the voltage is within specifications, proceed to the next test.

Load Test

1. With the engine running, turn on the blower motor and the high beams (or other electrical accessories to place a load on the charging system).
2. Increase and hold engine speed to 2000 RPM.
3. Measure the voltage reading at the battery.
4. The voltage should increase at least 0.5 volts from the voltage test. If the voltage does not meet specifications, the charging system is malfunctioning.

NOTE: Under and overcharging are typically caused by a defective alternator, or its related parts (regulator). The voltage regulator is internal to the alternator assembly in many vehicles. Faulty wiring and other problems can also cause the charging system to malfunction. Further testing, which is not covered by this book, will reveal the exact component failure. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.