2003 Ford Focus door lock fuse blowing

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  #1  
Old 04-15-17, 11:40 AM
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2003 Ford Focus door lock fuse blowing

A couple weeks ago the fuse on the automatic door locks on the car blew. I dug in and replaced the 20amp fuse and everything worked fine again - for a week. My wife just called to say the locks aren't working again. Before I make replacing fuses part of my weekend routine, is there a way to diagnose why that particular fuse keeps going? Is tracking down a short like this something I can do at my level?
 
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Old 04-15-17, 12:13 PM
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Welcome to the forums.

The biggest problem is trying to get the short to happen while you are working on the car. Many times it happens when the car is moving.

If the short is always there then it can be easy to find. You purchase a short finder kit. Pictured below. They run about $25 and most auto parts stores have them.

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You clip the circuit breaker across the blown fuse. The circuit breaker keeps automatically tripping (opening) every five seconds or so. That opening causes a magnetic pulse/field to be generated by the shorted wire. You take the meter which is nothing more than a magnetic gauge and hold/move it over the wiring harnesses. The needle will swing greatly if near the shorted wire. When the meter stops moving.... you've passed the short or the wire has changed direction.

For a door lock issue.... you would open the doors and put the meter near the thru door harnesses, then near the inside harness and then follow the bundles.

Since I do a lot of auto troubleshooting.... I've taken blown fuses and using a mototool I've ground the plastic to solder on wires. It's easier to clip the circuit breaker on the wires. You can also make up a set of wires with miniature crimp-ons that plug directly into the fuse box. I've got all kinds of things like this custom made to make the job easier.

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  #3  
Old 04-16-17, 07:31 AM
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I would advise you to take it to a Ford dealer. It could be a "known" issue to their national technical support - thus they may know exactly what to do to fix it.

Otherwise it is an advance electrical troubleshooting problem for a pro or a highly experienced person. This is because it is intermittent and you need to catch it in the act! And they would need factory wiring diagrams which is part of the factory service manual set of books/DVD's.

A common problem is a wire rubbing on a piece of metal somewhere - causing a short to ground. And with that said, very likely to happen at the door jamb where the door opens/closes, especially if the protective rubber boot has come off.

It would be *very* helpful to whoever is fixing it, if you can give as many details as possible, as to when this happens. Like after driving on a bumpy road. After numerous short trips and locking/unlocking the door a lot. Only when taking passengers in back seats. Never when just one person riding in car (and only drivers door being opened), etc.
 
  #4  
Old 04-20-17, 03:44 PM
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Actuator

Each of the door locks has an actuator, really a small electric motor. These can get "sticky" over time and the current draw to actuate can blow the fuse. Do you hear one of the locks click closed just a bit later than the others if you listen carefully when you do the door locking action? The trick is to isolate which one is sticking. The other approach would be to disconnect one latch at a time (tape up the wires), and see if the fuse does not blow after one is disconnected. If you go this route, you can also inspect the motor, you may have corrosion on the contacts where the wires connect, and this increased resistance can cause a fuse to blow, so might just need to clean up the contacts.

As per other posts, it could be a short where the wires go through the door into the body, the wire is constantly flexing and can surface abrade the wire jacket. So best to give a good look in the door jamb area while flexing the door back and forth and see if you can spot a problem.

But my guess is corrosion on an actuator motor contact. As the car gets older water can get past the various window wipes and into the door and even light barely visible surface corrosion can cause a problem, especially in cars that are outdoor stored.

The hillbilly solution would be to just try flicking the door lock on and off quickly say twenty times or so, might loosen things up, but in any event will vent some frustration!
 
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