Mechanics

FUSE

2000 Volkswagen Passat

Electrical problem
2000 Volkswagen Passat 4 cyl Two Wheel Drive Manual 170000 miles

The fuse that controls windows, sunroof, ignition, and other things keeps blowing. We believe there is a short in it somewhere. What advice can you give us in this problem. This is the second time is has occured. We replaced the fuse twice. It does not seem to cure the problem. Thanks.
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Kaytor
June 30, 2010.




Hi kaytor. Welcome to the forum. The blown fuses are not the cause of the problem; they are the result so they are going to continue to blow. There are a couple of ways to approach this. First, try to observe what is happening when it blows. If it blows when you activate a power window switch, note for which window. If it is only for the right front window, for example, inspect the wiring for that window. Frayed and touching wires between the door hinges is a common place to find shorts.

Fuses that blow at unknown times are harder to diagnose. What are you referring to when you include " ignition" in the list of affected items? Do you mean the engine stops running or do you mean other things that require the ignition switch to be turned on such as the radio or heater fan? The engine and radio are dandy things to be affected because you will know exactly when the fuse blows. If you can't tell when the fuse blows, only that it has blown when you try to activate something, you might be able to narrow it down by trying a different circuit first. For example, frayed and tangled sunroof cables can cause the motor to bind and blow the fuse. All you will know when you try to open it is the fuse is blown but you won't know it just happened. Open a window a few inches first to verify the fuse is still good, then open the sunroof. If you find it doesn't work, and now the windows don't work either, you can be pretty sure the fuse blew due to a problem with the sunroof.

These are tricks you can use to help find the circuit with the problem. The disadvantage to the mechanic is he doesn't have days or weeks to spend driving your car around looking for the problem. The disadvantage to you is you can waste a lot of fuses before you find the cause.

A different approach is to unplug various circuits to find which ones don't cause the fuse to pop. You can unplug window and sunroof motors but that still leaves their power wires in the circuit. Only some of the potential causes have been removed.

A better trick that few people know about is to use jumper wires to replace the blown fuse with a light bulb. The motorized circuits will not work because not enough current can get through the bulb, but when there is no short and no switches are pressed, the light bulb will be out or dim. It will be normal full brightness when the short is present. This makes a dandy visual indicator and it limits current to a safe value, all without replacing fuses over and over. Open and close doors, activate switches, unplug connectors, and flex wiring harnesses. The bulb will get bright when you do something to make the short show up.

When you say " this is the second time this has occurred", do you mean this is the second time you've had this same problem with blowing fuses or this is the second fuse that has blown? If it is the second fuse and it took a long time for the second one to pop, suspect touching or grounded wires as the most likely cause. If this is the second time for this ciruit to have a problem, typically you can expect to find a failed component such as a switch or motor.

Caradiodoc

Caradiodoc
Jun 30, 2010.


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