Mk5 12v Accessory Sockets (Cigarette Lighters) Dead Short

Hi Folks,

I know it's a long shot, but I thought I'd reach out to the experts on here to see if anybody has run into this problem before. I figure if there's a bad spot in this model where a wire chafes through, then mine shouldn't be an isolated incident.

My 2006 A5 Jetta has dead 12v charging sockets (cigarette lighter), etc. All three are dead, and there is obviously a dead short to ground as the 20a fuse blows instantly when the ignition is turned on.
The three sockets all look like new, and even with all three of them pulled and unplugged, the short is still there.
I've checked the 12v+ wire from the trunk outlet all the way to the a-pillar on the right hand side, and it is OK.

That leaves the center console wiring, and deep inside the dash, unless there is something that I'm missing.

I have the Bentley book, but there's nothing to see there. No plugs or connectors in the circuit other than the 3 outlet plugs. I'll run a new dedicated 12v+ wire from the battery if I have to, but I'd prefer to fix it properly if possible.

Rem

Hey Remy Martin.......

Did some asshole drop a coin in the lighter sockets?

Jack@European_Parts said:

Hey Remy Martin.......

Did some asshole drop a coin in the lighter sockets?

Click to expand...

Hey Jack,

Thanks for the reply. That may have happened previously, but the sockets are coin free now, and they look nice and clean...no burn or shorting marks that I can see. Even with all three sockets unplugged, the dead short is still there unfortunately.

I assume the 12v+ wire is chafed through to bare metal somewhere...I dunno. I can't really see where all the wiring goes to/from the fuse box.

Hey Jack (or anybody else that cares to answer),

I have torn this car into pieces following the wires in this circuit and cannot find a problem.

I did however find what I think is a diode in heat shrink. The Bentley diagram shows a "Blocking Diode" between 12v pos and 12v neg in this circuit. See picture below...I assume this is how VW places a diode in the circuit? So...my question is, could this diode fail and become a short? Lets assume that somebody (previous owner) dropped a coin in the cigarette lighter like most seem to do. In shorting out this circuit, is there a chance that this diode failed as well (and became a short to ground?).

If I don't hear back from you guys I guess I'll cut the wire and test it anyway.

https://postimage.io/app.phphttps://certificity.com

Bingo...we have a winner. I cut the diode out of the wire, and my dead short to ground is gone. Inside that heat-shrink is a IN4002 DC diode. Bench tested, it is full continuity in both directions...basically, a piece of wire.

So, this leads me to my next question(s): What is this diode for? And can I simply remove it and dead-end the two wires? According to my Mk5 Bentley book, this diode only showed up in this circuit in July of 2006...presumably for the 2007 MY gas Jettas, and "late build" carry-over 2006 model TDI's.

Thanks for any help!

well I would check short to ground, and continuity (to the remote ends) from either side of the wires before you splice them together.

the diode may be busted, but it may not be the source of the short either.

Rembrant, would you mind positing the section of the WD from the Bentley that shows where this diode is located in the circuit?

I'm trying to understand what its purpose is, and whether it could indeed be the source of your short.

-Uwe-

Uwe said:

Rembrant, would you mind positing the section of the WD from the Bentley that shows where this diode is located in the circuit?

I'm trying to understand what its purpose is, and whether it could indeed be the source of your short.

-Uwe-

Click to expand...

Hi Uwe,

The diode appears to be the source of my dead short. I've removed it, terminated the +12v and -12v wires, and the circuit now works fine.
Bench tested, the diode shows full continuity in both directions.

I'm using the 2005-2010 Jetta Bentley Book.
Electric Wiring Diagrams EWD-185
Standard Equipment (from July 2006)
Wiring Diagram No. 69/15
J29 - Blocking Diode
(Is this what you meant? Or did you mean for me to post an image of the diagram?)

I was talking to a friend, and he said that the diode must be for "back EMF", when you either unplug a 12v charging device, or turn the ignition off when a 12v charging device is in use?

In my car, this circuit is powered with the ignition on, from J519. According to the Bentley book, the Mk5 cars built before July 2006 did not have this diode, but they look like they were powered all the time (bypassing J519).

Would appreciate your thoughts on what the purpose of this diode is, and how critical is it?

I once came across a blocking diode on a coach air conditioning clutch power supply to direct the supply to ground should a spike occur thus blowing the fuse ,I disconnected it replaced the fuse it worked fine,ordered and fitted the diode sorted.

Did you use a jump starter between sockets a diode only passes supply in one direction ?

OK, terminal 75A would indeed be a circuit for the lighter(s), and that diode is clearly intended to prevent flow down current track 193, so it makes perfect sense that if this diode is shorted, the fuse for the lighter(s) would blow.

But that still leaves me puzzled as to what's on current track 104 (which 193 leads to)?

-Uwe-

Uwe said:

OK, terminal 75A would indeed be a circuit for the lighter(s), and that diode is clearly intended to prevent flow down current track 193, so it makes perfect sense that if this diode is shorted, the fuse for the lighter(s) would blow.

But that still leaves me puzzled as to what's on current track 104 (which 193 leads to)?

-Uwe-

Click to expand...

https://postimage.io/https://certificity.com

Hello Remy Martin.....

It is installed to absorb a backward spike especially if someone is installing a DC to AC inverter in the sockets to run a laptop etc. creating "heat" through latent resistance of constant load.

This diode/thermal protection sort of fuse pops to ground or considered a failure mode, this additionally helps prevent a load that will heat up the circuit due to pulling just enough current to heat the wire, but not enough AMPS to blow the fuse.


https://en.wikipedia.org/wiki/Failure_of_electronic_components

Helps stop fires!

But that still leaves me puzzled as to what's on current track 104 (which 193 leads to)?

Click to expand...

It's just the ground for the socket to complete the connection for the load device used by the accessories & the socket illumination bulb.

Hah! So the other side goes to ground. Indeed, the only purpose that diode can have is to shunt negative spikes to ground, which would prevent damage to other items on the same circuit should such a spike occur.

-Uwe-

Thank you gentlemen for your replies. Much appreciated.

I'm OK with wiring, but electronic components are not really my thing.

I'll grab a new diode next week, there are a couple electronic shops close to my office.

For anybody else that comes across this thread in the future, the diode is in the center console wiring harness, right next to the accelerator pedal.
(North American model).

Peace & Axle Grease,
Rem

The diode is hardly essential. Everything will work without it.

-Uwe-

Uwe said:

The diode is hardly essential. Everything will work without it.

-Uwe-

Click to expand...

That's good to know Uwe, thanks!

I have the car all back together now, and so far the circuit is working great. I sure did put a lot of hours into this one...lol, good grief. It gave me a chance to clean all of the center console parts and pieces individually, so I'm happy to have gotten that done at least.

Thanks again guys.

That's good to know Uwe, thanks!

I have the car all back together now, and so far the circuit is working great. I sure did put a lot of hours into this one...lol, good grief. It gave me a chance to clean all of the center console parts and pieces individually, so I'm happy to have gotten that done at least.

Thanks again guys.

Click to expand...

You could also just install a lower amp fuse and be IDK common sense mindful....................

Jack@European_Parts said:

You could also just install a lower amp fuse and be IDK common sense mindful....................

Click to expand...

Haha...yes, I suppose so. I could probably get away just fine with a 10a fuse in the circuit for what I do. I keep an iPhone charging a lot of the time, and once in a while one of those Koolatron coolers in the trunk (4 amps?). Worst case scenario would be charging two iPhones at once if I had somebody with me, but that would be a rare case.