How To Test For A Bad Diode In Alternator

July 14, 2017

The best way to identify alternator problems is by conducting a bench test. If the alternator fails any test category your customer needs a new alternator.

How To Test An Alternator In Under 10 Minutes

Diagnose Starter Alternator Problems

Alternator Failure Causes

Set the multimeter to its diode test mode denoted by the circuit symbol for a diode which looks similar to an arrow.

How to test for a bad diode in alternator. To test for this condition switch the voltmeter to ac voltage with the engine at about 1200 rpm the meter should read 0 volts. Any amount of ac voltage would indicate a bad diode so youll need to replace the alternator. If the headlights flicker dim or get brighter when the accelerator is pressed down your alternator may be bad.

To check for a possible bad alternator diode switch your voltmeter to a low setting on the ac alternating current voltage scale. Your voltmeter should read 0 ac volts. If voltage is present one or more diodes has failed and the alternator should be replaced.

A bench test will check the diodes and internal regulator and then tell you if the alternator is capable of producing its rated current and voltage. To perform the headlight test start your car and turn on your headlights. With the engine running touch the meter probes to the battery terminals.

With the engine running touch the meter probes to the battery terminals. With the vehicle in park press on the accelerator while a second person observes the headlights. Please watch the following video below to watch the test being performed by one of our mechanics.

Heat the solder pad around the diode leg until the solder is molten and then gently pull the leg through from the other side using pliers. Your voltmeter should read 0 ac volts. Soak up any excess solder with desoldering braid leaving the hole clear.

To check for a possible bad alternator diode switch your voltmeter to a low setting on the ac alternating current voltage scale.