What does open diode on fuel wiring harness mean? Does it mean that there is a cut in the wire?

I had a new radio and overhead dvd installed and then the fuel gauge did not work but the audio shop what they did would not impact the fuel gauge at all. Does it mean they most likely tapped into the fuel guage power wire?



Jim

 

A diode is a device that allows current flow in only one direction. Each diode has a rated voltage that it will work to...that is to say that if you reverse bias 12V (of opposite polarity to the diode) across a 4V diode , it may conduct anyway (called breakdown or reverse breakdown)...most likely damaging the diode and causing it not to conduct at all (open), or conduct all the time(short).

The same it true for undervoltage to a diode. Each diode has a certain power (watts=voltage x current x power factor) (power factor is 1 for almost all DC applications) that it is rated for. If voltage that is passed thru the diode drops significantly, the current flow will raise accordingly to keep the power equal..this could damage the diode as described above.

If the diode was forced into it's breakdown region by placing too great a reverse bias potential across it, it could open(or short for that matter). They may have nicked a power lead and shorted it to ground without knowing it...or may have just knocked something loose back there...or it could be completely unrelated to the install.

I know that's a whole lotta stuff to read without a very good answer, but hey... now you know a little more about diodes...

I recommend checking out your haynes/chiltons/factory repair manual to see what tests you can do to find out if your fuel level sending unit and such are working properly b4 going after the audio install company...they can be really stubborn and the checks that you perform on your vehicle may be really easy and quick.

-Dan

 

The dealership says that I need a new fuel guage wiring harness, which they say only impacts the fuel gauge, so it is not the wiring harness for everything.

Should this fix it?



Jim

 

if the dealership says its the reason, then it probably is. I say probably b/c a dealer tried to charge me $188.00 for putting my truck on the machine and coming back with " I dunno" as the $188.00 answer.

A new harness seems a bit extreme, and unless they plan on ripping out the old and splicing in the new, it seems like a lenghty process to replace. Maybe there is a built in diode in the harness that can't be replaced without a new harness?

Have you pulled the instrument cluster to see if there is anything obviously wrong with the existing harness?? I've seen some botched install jobs by ppl who just didn't know what they were doing, or doing things for the first time... but a reputable install company shouldn't hack your electrical.

Where did you get the information that a diode was bad??

BTW what kind of vehicle are we talking about here? Please include year/engine/model and trim.

-Dan

 

This is an 06 supercrew 5.4, 4x4, I just had an overhead dvd installed and a new radio and then the fuel guage stopped working. The person who pulled it in to work on said it said low fuel when he got in it, so it could be coincidence between when I dropped it off and when he got in it, that it went bad.

The dealership said it is an open diode in the fuel guage wiring harness.

I justed wanted to make sure that it was just the wiring harness for the fuel sensor like the dealership says they said there is an open diode, and the audio shop is a very reputalbe shop that is where the dealership takes there aftermarket dvd installs.

Should I take it back to the audio shop to let them determine if it anything they did or should I just let the dealersip work it out.

The audio shop the new deck got the power and ground from the radio wiring harness and the power for the overhead dvd would just come from the wiring harness for the radio.

 

The trim is XLT.

 

With nothing really concrete to go on for the fault, a diode is usually accross a circuit to prevent voltage spikes from getting back to the electronics that do the display, for protection. Sometimes they are used for circuit isolation when two actions are controlled on the same circuit.
The dash has a micro processor that needs these protections.
If it is a diode, it sounds like it is shorted, killing the signal back to the dash.
They know where the diode is but the question is why not fix it instead of changing the whole harness.
Two reasons could be that it's Ford's reccomendation to change the harness by standard procedure in there troubleshooting and that the dealer won't allow that kind of work so can't fix it on a componant basis.
Just an opinion based on a lot of life's experience as to why they think the harness must be changed.
BTW, no audio installation should ever tap into a vehichles electricals to power an aftermarket system unless it is a replacement to the same function.
Otherwise it should come from a properly fused and controlled tap off the fuse panel.
If not, you get whatever happens afterwards.
Making any other installations controlled by some function already on the vehichle calls for someone who understands what has to be done so it works without causing a fault.
Good luck.