How hard is it to diagnose an electrical problem on a Volkswagen (please read before answering)?

I have a 2003 Volkswagen Jetta GL 2.0 with almost 118,000 miles. Just recently, it would not start up. When I tried to start it up, it made a rapid clicking sound. I was able to get the car jumped and I took it to an auto parts store. The manager there ran a test on my battery, alternator, and starter. He told me that the battery and alternator were perfectly ok. He said the battery was ok too, but that a faulty module within the car drained some of the electricity from the battery. He told me that if I drove the car around for a while, it would recharge the lost electricity on the battery. I took his advice and after 1/2 hour it was fine. He said I would have to take it to a mechanic to find the faulty module. How difficult is it to diagnose an electrical problem on a Jetta like the one I have? I was talking to someone who told me that all a VW mechanic has to do is hook it up to a computer to detect the faulty part. Is this true? Or will diagnosing an electrical problem be more complicated than that? If so, what will it take? I would really appreciate input from anyone who's experienced on the matter. Thanks in advance.

3 Answers

  • Briano
    Lv 5
    8 years ago
    Best Answer

    You have a parasitic Drain, or a resistive ground.

    Finding the circuit that has the drain is a exercise in hunt and pecking.

    Usual Suspects are, After market alarms, After Market Radio installation.

    How to find?

    Buy a Ohmmeter Digital is fine they run about 6 bucks or so for the cheap ones.

    Car off.

    Remove the Negative battery lead off the car.

    Probes for the meter in the AMP circuit, that is one in the ground (black) and the other in the amp slot. Position the meter to read AMPS......

    Place it as the Negative lead on the disconnected battery cable.

    Positive lead on the Negative post of the car.

    Turn the meter on.

    Read the meter.

    Now one at a time take a fuse out of the fuse box, and read the meter better, as in closer to Zero?

    in not replace that fuse and pull the next one, better? no, you have to replace it and pull the next one... It is a process of elimination to get to the circuit that is causing you grief. Once you know what the fuse controls, then looking at the schematics of the cars wiring diagrams will get you to figure out which offending thing it is.

    DO NOT SWITCH the meter while you have it in the AMP modes.... It will fry the meter.

    Now all of this sounds simple and it is, but that is how most auto electric shops will look for a parasitic drain.

    Take it to the Dealer, or and automotive electric shop.. It may take them a while to find it...

    Most Service Centers for Autos aren't geared to find electrical issues....

    But you will need the Bentley Manual for your car, and the cheap meter, and a few hours work.

    to find the circuit. Maybe you can have a buddy come over to assist for a few beers after.

    It can appear Daunting and quizzical but it just simple diagnostics.

    A fundamental primer on electrics is here:

    Source(s): 40 years of playing with Electronics, and Cars.
  • 8 years ago

    Briano gave a great answer.

    I would just add that you can get a working volt meter at Harbor Freight for $3.

    And if you have a test light, that can be used instead.

    The brightness of the bulb indicates voltage and current.

    If there is a drain, the test light between a battery terminal and its cable clamp will light up.

    The alternator itself is one possible drain.

    The battery can also have an internal drain, which you would discover if it also went dead over night, even when out of the car.

  • najar
    Lv 4
    3 years ago

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