Generator Diagnosis

Generator Diagnosis

Before beginning any generator diagnosis, ensure that the battery is in good condition and has passed all testing procedures. A weak or detective battery will influence the generator testing.

The generator may be tested using:
- DISplus
- VAT testing equipment.

Workshop Hint
Before beginning diagnostic procedures on the charging system do the following:
- Run engine at idle speed for about 5 minutes.
- Switch off all electrical loads.
This is done to ensure the battery is charged to such a level that the generator will not be fully utilized and that loads required during starting (e.g. starter; secondary air pump) will be already switched off.

Testing Generator With DiSplus

Two modes of testing are available when using DISplus.

- Testing using Test Plan
- Testing using Preset Measurement

Testing Generator Using Test Plan







Testing the charging system using a test plan is the more complete method of testing.
When selecting this mode of testing, other components in the charging system are tested in addition to the generator.

Test plans available:
- Generator (Checks voltage and current output)
- Wiring from generator to battery (Performs voltage drop test)
- Charge indicator lamp (Condition of bulb, wiring and signal to bulb)
- ON delay and Start ON delay (If applicable)
- Ground side circuit wiring (Voltage drop test)

Sub-tests may be available with some of the component testing.

There are many advantages to using the test plan.
1. Complete system testing.
2. Functional description of system on screen.
3. Proper wiring diagrams provided during testing.
4. Test instructions and notes.
5. Instructions for proper test set-up.
6. Display of nominal values.
7. Solutions.

Testing Generator Using Measurement System




Enter the measurement system and select Preset Measurements.
Instruction on the proper hook-ups required are available through the HELP button, selecting Help using Preset Measurement.

The oscilloscope will display preconfigured for the testing.

Diagnostic information available through oscilloscope.
- Voltage Graph.
- Charging Current.
- Harmonic Content.
- Rotation Speed (Engine RPM).

Harmonic Content

This is an expression of AC voltage contained in DC voltage.
The higher the percentage of harmonic content the larger the amount of residual AC voltage in the DC voltage High residual AC voltage is caused by weak or failing diodes in the generator. Generators which have harmonic content readings higher than specified (In TIS) should be replaced.