GM Service Manual Online
For 1990-2009 cars only

The generator bench test requires a standard Generator Test Stand in order to operate the generator. A fully charged battery is also required.

  1. Install the generator to the test stand.

  2. Object Number: 1049  Size: SH
  3. Connect the generator.
  4. • The carbon pile must be turned OFF to begin the test.
    • Ensure that the generator BAT terminal is connected to the positive battery terminal (through the ammeter).
    • Make sure the battery is grounded.
    • Make sure the generator is grounded.
  5. Connect a 30 ohms-500 ohms resistor between the positive battery terminal and the (L) terminal on the generator.
  6. Operate the generator through the test stand.
  7. • Increase the speed slowly while observing the voltage.
    • Uncontrolled voltage that increases to above 16 V indicates a shorted rotor field. Or the voltage regulator is not working properly, or both.
    • A shorted rotor field coil can cause problems in the voltage regulator.
  8. If the voltage is below 16 V, increase the generator speed while adjusting the carbon pile (to obtain the maximum amperage output).
  9. Maintain the voltage above 13 V.
  10. • If the measured output is within 15 A, of the rated generator output, the generator is good.
    • If the measured output is not within 15 A of the rated output, replace the generator.