Check for voltage at the alternator connector at the D+ terminal, with the harness unplugged from the alternator and the ignition in the on position (Blue wire), using a Digital Volt Ohmmeter (DVOM). Battery Positive Voltage (B+) should be present.
Check for battery voltage on the B+ wire.
Check for alternator case ground.
Check for a voltage drop between the alternator and the battery by placing the red lead of your meter on the alternator B+ terminal and the black lead on the battery B+ terminal. Should have approximately 0 V voltage drop.
Test the battery for load capacity.
Put a test light between the B+ post at the battery and the D+ connection at the back of the alternator (put test light in place of the D+ wire): A. When connected, test light should be on. The test light is taking the place of our battery light in the dash and this simulates the bulb check. B. Start the vehicle. When the internal revolutions of the alternator reach approximately 600 RPM, the magnetic field generated should be great enough to interrupt the ground path. The test light must go out. If the test light stays on or is flickering, there is an internal issue inside of the alternator.
If voltage is available to the D+ terminal, good ground is available, no voltage drop across the power circuit and the alternator will not charge, a faulty alternator is indicated.
On later model vehicles, the D+ wire was replaced with the L wire. For all intents and purposes, D+ and L are interchangeable.
Confirmed Fix Summary highlights that the most popular fix for this issue is to replace/repair alternator and inspect wiring across most common models.
Bill started his automotive career at an early age. He attended the small engine class and also spent 2 years in the high school automotive shop learning the basics of automotive repair. He also worked for an independent Goodyear dealer during this time. After graduation, Bill spent 2 years in Chicago completing the Automotive and Ford Fact programs with Universal Technical Institute. After graduation, he then went on to the Audi Academy where he received factory specific training. Bill spent 4 years in North Carolina working as a technician at an Audi dealership;. It was here that he achieved Expert status as a Audi technician while facing the many challenges of automotive diagnosis that today’s cars provide. Bill is currently an Audi/VW specialist with the European Carline.
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