# Fuse 16 Keeps blowing



## lite1979 (Sep 9, 2005)

*Fuse 16 Keeps blowing [SOLVED]*

*** Final Edit *** Solved

One of the wires going into t4 on the Fan Control Module was rubbing against the frame and shorted the internals of my after-run coolant pump.

I fixed the wire that was rubbing against the frame and replaced my after-run coolant pump, and my TT has been running like a champ.


*** Edited ***

As stated in the title, Fuse 16 keeps blowing in my 2001 Audi TT Quattro Coupe 225. The fuse basically powers the Fan Control module, so it's used for the magnetic clutch on the A/C compressor and the after-run coolant pump on our cars. It also supplies power to the G65 A/C pressure switch (this can be confusing, as the VCDS scan will always say F129 switch open circuit - G65 is a newer version of F129 with three wires instead of four). 

I've checked continuity from the magnetic clutch to the Fan Control Module, and it's fine. Same for the after-run coolant pump and the G65 A/C pressure switch.


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## lite1979 (Sep 9, 2005)

For what it's worth, I'm investigating this. The wiring diagram with this fuse in is is on page EWD-79 of my Bentley manual, and it shows the following: 

J293 (Fan Control Module) to a red/grey wire
red/grey wire to Fuse 16 (10 Amps)
Fuse 16 to red wire to A98 = plus connector -4- (30) in instrument panel wiring harness
red wire to B156 = Plus connector -4- (30) in wiring harness interior


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## B1-16V (Aug 5, 2002)

Curious what you've tried.

Have you tried not having your AC on, (keep it on "economy") for a while? If so, does it still blow the fuse?

If fuse stays good, does it immediately blow when turning on AC?

Have you verified if the AC is actually working? 

Obviously all those questions are 100 percent related. That's where I'd start.


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## lite1979 (Sep 9, 2005)

Thanks for asking!

Edit: Fuse blows and battery dies whether or not I have A/C on.

A/C does not work.

What I've done so far:

replaced the F129 switch

replaced the radiator fans

replaced the radiator thermo-switch for the fans

replaced the Fan Control Module under the battery

replaced fuse 16 several times now

checked the voltage between pins 1 and 3 for the F129 switch with A/C on; voltage jumped around and the battery died very quickly after that.


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## lite1979 (Sep 9, 2005)

Checked resistance at the A/C clutch coil, and it's good - 3.8 Ohms. Checked at the after-run coolant pump as well, but I'm not sure what that's supposed to be - came out to 1.2 Ohms.

Still feels like looking for a needle in a haystack, but I'm thinking of borrowing one of those powered current checkers now - apply power to the fuse location, then use a tracer to see where it stops. I've seen people use them on youtube videos, but I've never used one myself...


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## 20v gti guy01 (Jan 31, 2015)

I would check your wiring to the alt and pump. This sounds like you have a wire grounding. 


Sent from my iPhone using Tapatalk


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## lite1979 (Sep 9, 2005)

I agree. I definitely have a short to ground, and that's what's blowing my fuse. 

Wiring for the alt looks good, but I haven't taken it apart (it's bundled with the wiring for the A/C clutch coil, wrapped in a tight rubber tube).

Wiring for the after-run coolant pump looks good, too, but it joins up with a bunch of other wires on the other side of the motor, so I'm still trying to figure out where the two sides meet. I think it's behind the motor somewhere, and I did do a bunch of work back there between rebuilding the turbo and replacing the downpipe/cat.

I've also had the transmission and bevel box out twice in the last few years, but all the wires on TOP of the transmission look good.

I hope we have today's weather again tomorrow, as I have the whole day 'off'. I still have to work from home, but I don't have to tend bar.


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## lite1979 (Sep 9, 2005)

So I started testing continuity from G65 (a/c pressure switch), N25 (a/c clutch coil), and V51? (not sure; manual's not in front of me, but it's the After-Run Coolant Pump.

I basically set my multimeter to continuity, and watched the numbers drop as I confirmed known grounds, and supposed open circuits.

They all report no continuity on positive, no continuity on data, yes continuity on ground (I used the intake manifold for my ground in each case as it's right there).

Remove battery, remove battery tray, remove new-ish J293 (Fan Control Module). 14-wire plug looks clean. 4-wire plug looks clean.












I mocked the J293 (Fan Control module) back up in its installed position, and I can say that this wire was definitely touching the frame right next to it.

I plan to put everything back together tomorrow and see what's good, but I bought five new fuses just in case.

Edit: Not sure what's up with sharing a google image on here, but I'll fix it eventually so you can see the open wire.


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## lite1979 (Sep 9, 2005)

Can someone tell me if the picture above is visible?


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## lite1979 (Sep 9, 2005)

After wrapping that up and putting everything back together, I'm still blowing fuse 16.

Fuse 16 blows as soon as I turn the ignition on, in fact.

I'm wondering if the short circuit fried my Fan Control module...


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## [email protected] (May 27, 2004)

lite1979 said:


> Can someone tell me if the picture above is visible?


no photo on my end. 

if it's blowing on key on, it has to be a dead short. see what is on the 15 feed for that circuit (15 is key on +, 30 is + whenever the battery is hooked up etc)


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## lite1979 (Sep 9, 2005)

Thanks. I'm thinking my short may be in the dashboard, then.


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## lite1979 (Sep 9, 2005)

So though I fixed that wire, I think there's still a short _inside_ my Fan Control Module. Once I disconnected it, Fuse 16 stopped blowing.

The module is relatively new, but I think that bad wire messed up the FCM since I didn't know about the short...


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## [email protected] (May 27, 2004)

sounds like you're on the right track. you don't have a stuck fan do you? as in, the fan itself could be internally shorted


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## lite1979 (Sep 9, 2005)

Image fixed. Had to create an imgur account, but I hope to be more active on here to make it worth it. 

Both fans spin just fine (and they're only three years old at this point).

I'm waiting for a new FCM to come in the mail, then hopefully I can mark this thread as solved. 

What happened, if I understand correctly, is that wire was touching the frame, and in turn fried my Fan Control Module. I didn't know this was the reason my fans were staying on after shutting the car off, so I was checking for a parasitic drain.

Naturally, in my process of checking for a parasitic drain, pulling fuses at night time checking to see if the amperage draw went to zero didn't help, because when I pulled fuse 16 it was already blown.

When fuse 16 blows, the car makes the fans run all the time, because the Fan Control Module isn't in control anymore, and it's better to have a dead battery than to have a warped head from overheating, I guess.

I replaced a bunch of stuff thinking the parts were bad, like my G65 A/C pressure switch (at the recommendation of the place that charged up my refrigerant). They were able to apply 12V to the A/C clutch coil and get cold air, so I figured either the radiator thermo-switch was bad or the FCM was bad. I replaced both, and still couldn't get cold air, and that's when I read about fuse16 and how the fans work if it's removed/blown.

Hopefully I don't have to replace either the G65 or the radiator thermo-switch again once the new FCM comes in. I'll update when I get it.


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## lite1979 (Sep 9, 2005)

Update:

New FCM came in today. Installed it, hooked up the battery, fuse 16 blows. Grrr.

Pulled the 30A fuse for the fans on top of the battery - fuse 16 does not blow. At this point, I think my short to ground has to be between the FCM and the fans. Am I right?


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## [email protected] (May 27, 2004)

lite1979 said:


> Update:
> 
> New FCM came in today. Installed it, hooked up the battery, fuse 16 blows. Grrr.
> 
> Pulled the 30A fuse for the fans on top of the battery - fuse 16 does not blow. At this point, I think my short to ground has to be between the FCM and the fans. Am I right?


that's why I asked about the fans...

even if they spin, they could be internally shorted (low speed to high, low to ground etc) 

I would put it all back together, put in all fuses, FCM etc and disconnect the fan(s) if the fuse(s) don't blow I would suspect the fan(s) are NFG


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## lite1979 (Sep 9, 2005)

Fuse 16 still blows with the radiator fans disconnected (at the two 3-wire junctions, one female, one male).

I'm going to inspect the wires going from T4 to its respective endpoints. Wondering if the radiator thermo-switch could be internally shorted?


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## lite1979 (Sep 9, 2005)

Disconneting the radiator thermo-switch STILL blows the fuse.


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## lite1979 (Sep 9, 2005)

Just disconnected the T4 from the FCM and tried again - fuse does not blow when T4 is disconnected. I think this suggests that the wires from T4 are grounded somewhere.


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## lite1979 (Sep 9, 2005)

I'm still tracing the wires, and I don't see any clear evidence of shorts to ground. I'm behind the left headlight now, and this ground kind of stuck out to me:


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## lite1979 (Sep 9, 2005)

I'm losing my mind on this one.

I traced all four wires from T4 at the FCM to their respective destinations, and not one of them shows any sign of touching ground, anywhere.


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## B1-16V (Aug 5, 2002)

You'll figure it out eventually. So many of us have been there for one reason or another. Wish I had more than just words of encouragement.


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## lite1979 (Sep 9, 2005)

I was thinking, since it doesn't blow until I turn the ignition on, maybe I'm looking at this the wrong way.

Ignition switch goes to Plus connection (15) in instrument panel wiring harness on a 2.5mm black wire.

That black wire goes to fuse 5 (7.5 amps - fuse is fine) on the left of the dash. - if the fault were in this circuit, the 7.5 Amp fuse would blow, correct? It doesn't though, so I think that once the fan relay in the FCM is activated, that's what causes fuse 16 to blow. Low power from ignition activates the relay, high power from the fan circuit goes back through the FCM to a peripheral with no resistance, which in turn blows the fuse.

From the fuse panel, a 0.5mm black/blue wire goes to B135 connector inside dash board, and splits to both G65 in the engine bay (A/C pressure switch), and T17 behind instrument panel > D/9 at the HVAC control head.

I'll trace the wires from the ignition switch and report my findings. It's also possible that the G65 wiring is to blame, since that's on the same circuit, but when I tested for continuity on the G65 connector, ground was continuous, and neither the data nor the hot wire showed continuity to ground. Perhaps that because the ignition was off when I tested.


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## lite1979 (Sep 9, 2005)

My next step is to remove all of the wires from T14 except the red one (power). If the fuse doesn't blow, then I'm re-connecting each wire to T14 until it does, then chasing that wire down for cracks/missing insulation...


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## B1-16V (Aug 5, 2002)

Wow, what a pain.


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## lite1979 (Sep 9, 2005)

Just bumping to let everyone know I haven't given up 

I'm getting stuff done, just not on my TT. I got solar panels installed on my roof last week!

I couldn't get the pins out using paper clips or needles, so I have a special tool on the way. I've wasted $20 on worse things.


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## lite1979 (Sep 9, 2005)

Just a little update again. I drank too much coffee, so I'm outside thinking of what I can do to figure this out. I got the tool to remove the pins one by one, but I'd prefer to have a friend help me with that, since you have to have the battery hooked up and be prepared to blow fuses, and the location of the Fan Control Module makes that kind of difficult, being underneath the battery tray.

So what I did was say "if there's a short to ground somewhere on the 14-pin connector to the Fan Control Module, then there should be no resistance from ground to that pin, correct?

Sure enough, pin 1 beeped when I touched the multimeter to ground and pin 1....... It's a red/black wire, and I lost the good PDF I had to explain where it goes, but I'm looking in the Bentley for it now...

So the red/black wire goes to the after-run coolant pump. Multimeter shows 1.7 ohms; I'm not sure if that's normal or not. Anyone know what the resistance should be for this motor?

I keep getting interrupted by a redirect on this site, too. Keeps navigating to a scam site. 

Edit:

So far, all of the resistance values are matching up with their respective endpoints. After-run coolant pump is within spec, A/C Clutch is within spec. The only one that reads 0 Ohms is the ground wire...


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## QCOUPETT (Dec 21, 2012)

*Have you replaced the after run pump?*

I know you have checked it and everything "seems" fine, but on my coupe I was having trouble with no cold air from my A/C (a big problem in Texas) for months. Fans checked out OK but my indie ultimately pulled the small fan and looked inside and it was all messed up in there, was intermittently working and giving positive readings. Might be worth trying, as electrical gremlins are sometimes hard to find.


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## lite1979 (Sep 9, 2005)

The fuse blows even when the fans are disconnected...


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## QCOUPETT (Dec 21, 2012)

*OK*

I spoke too soon. When I picked the car up I started it then turned it off. Fans were not running so I thought I was golden. Drove it about 1/2 hour back to the office, and when I turn d it off fans were running again. Keeps blowing fuse 16 like yours. Taking it back Monday. Frustrating but I am sure you can relate....


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## diptenkrom (Apr 1, 2018)

i have a question, as i am having part of the issue you are having. Does your ac clutch stay engaged? i had battery drain from that pullin gpower constantly, and i had to unplug it to keep battery from dying, and i didnt have functional AC either. still a problem i will have to figure out, hopefully the FCM will be the culprit, otherwise i will start pulling out my hair. 

basically i am saying unplug the connector from the AC compressor and see if it stops blowing fuse/draining battery


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## lite1979 (Sep 9, 2005)

Isolated to the black/blue wire at 9 on T14.

First, I soldered a 10 amp fuse to two pieces of layover wire. I hooked up battery negative to battery terminal negative via jumper cables, then I removed t14/4, aka constant power, and used my layover from the Fan Control Module to the battery positive to make sure that wasn't the source of the short circuit.

Test passed, and the fuse did not blow. Knowing that, I proceeded to remove the rest of the pins, then replace them one at a time until the fuse blew.

Tracing the black/blue wire now - I think it's the A/C clutch coil, but I'll post when I'm sure.

Apparently you can hammer down some paper clips to get the pins out, but dropped $20 on a tool to make it easier.


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## lite1979 (Sep 9, 2005)

So, it turns out that the black/blue wire is actually switched power from the ignition - not likely to be my ground fault. Next step is to see if the fuse blows with just pin 4 - constant power, and pin 9 - switch power connected and 'ON'.

If it doesn't, I'll re-connect the rest of the wires (1,2,5+14,6,7,8) and see which one causes the fuse to blow then follow that. 

Almost there......


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## lite1979 (Sep 9, 2005)

So with pin 4 (constant power), pin 9 (switched power), and pin 6 (ground) connected to the FCM, key in the "ON" position, the fuse does not blow, but once I add pin 1 (V51 - After-run Coolant pump), the fuse blows.

This leads me to believe that my short to ground is somewhere on this wire. Unfortunately, it travels up to the rain tray on the driver's side, across the rain tray, and back down the other side of the engine bay, so it's very long, and will require a lot of work to inspect.


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## QCOUPETT (Dec 21, 2012)

*Is this feasible?*

Just run a new wire?


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## lite1979 (Sep 9, 2005)

That's a possible solution. I want to make sure the pump isn't the source of the short circuit, too. I'm going to use a test light with ground hooked up to the battery and a test light on positive with this wire removed from the pump. If it lights up, that's my short circuit.

I also want to apply 12V to the pump to make sure it still works. There's some crust on it, so it may have failed or be leaking. If it doesn't work, I'll get a new one from germanauotoparts.com (they're back!).

Of course, all this leaning over the engine bay has killed my back, and I don't want to get too dirty before I head into work at 5pm tonight...


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## QCOUPETT (Dec 21, 2012)

*Have you*

Applied power to the a/c compressor and does the clutch engage? My indie has finally found (I hope!) that the breaker in there was tripping, and then etc, etc, etc. Replaced the A/C compressor. Your issue may be different, as electrical issues can be that way.


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## lite1979 (Sep 9, 2005)

I got your PM, thanks! My fuse blew before I got to the A/C clutch coil wire, so I don't think that's it, but I can definitely check the clutch coil for action. I'll try applying 12 volts to it when I test the After-Run coolant pump. It worked last time I had my A/C serviced, though, but because of this short circuit, I couldn't get A/C to work without jumping the coil...


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## QCOUPETT (Dec 21, 2012)

*OK*

Just picked my car up. AC was cold, drove it back to the office about 20 miles, turned it off- NO FANS RUNNING !!! We replaced the AC compressor, they bench tested the old one, coil was fried. Hope you figure it out soon.:thumbup:


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## lite1979 (Sep 9, 2005)

Still chugging along here. It snowed all day yesterday, so I stayed inside, but I decided to put on my Carhartt jacket and go out before I head to work at 5pm and do some tests.

I couldn't get the pins out of the pigtail for the After-run coolant pump, so I haven't checked it for operation, but I did do another resistance test right at the pump and it was 0.8 Ohms. I think that's low, and probably the source of my short circuit/blown fuse. I got 0.2 Ohms just from touching the leads for my multimeter together.

I tested the red/black wire for a short to ground by hooking up battery negative, then running battery positive to a test light (screwdriver style) with an in-line 10 Amp fuse that I used for a previous test. No light! that means that this wire is not shorted to ground.

I most likely need a new after-run coolant pump, so I'll order one now in anticipation, but I want to test the other leads from the FCM one-by-one before I exclude anything else.


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## QCOUPETT (Dec 21, 2012)

*On mine.....*

I had blown both the after run pump and the a/c compressor coil.


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## lite1979 (Sep 9, 2005)

Hooked up the new after-run coolant pump and the rest of t14 and the fuse is good! I still have to hook up the fans and radiator thermoswitch and do some wire-wrapping, and put my windshield wiper arms back on (I took them off to get into the rain tray in case I had to follow a wire up there).


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## QCOUPETT (Dec 21, 2012)

*Glad you finally sorted it out!*


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## B1-16V (Aug 5, 2002)

So, that was it? Just the after run pump?


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## lite1979 (Sep 9, 2005)

It was the after-run coolant pump, but it was fried because of the first short circuit, which was one of the wires in T4. When that hot wire touched the frame, it sent enough current through the after-run coolant pump to melt some internals, causing a short circuit.


If it ever stops snowing/raining here, maybe I'll get this car together.


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## lite1979 (Sep 9, 2005)

So while Fuse 16 is rock solid, it appears that my fans aren't working like they should. I still haven't replaced the FCM, which may have been fried in the process as well. I'll test the fans again using the thermo switch method first, but I also have a parasitic drain that I have to tackle...


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## lite1979 (Sep 9, 2005)

So maybe I'm tracking down ghosts. No parasitic draw when tested using the 10 Amp un-fused in-line multimeter - CD changer caused some action at first, then it dropped to .05-.00. 50 milliamps isn't enough to drain it overnight, so maybe I just need to drive it more.

Regarding the fans - I replaced the Fan Control Module with a new OEM unit, and I still have no fans. Pulling fuse 16 makes them run, so I'm not sure where my disconnect is.


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## misiu.ryb (May 21, 2015)

Hi, 

I am really impressed with your investigation. I am building a track car and would like to ask you about installing a manual switch with the fuse in place of fuse #16. I would like to get the fans running continuously when I am using car on the track. I have found out from your investigation that pulling fuse 16 will make both of the fans running, could you tell me will the after-run coolant pump work also?

Cheers,
Mike


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## lite1979 (Sep 9, 2005)

Pulling fuse 16 will _prevent_ the after-run coolant pump's operation. I wouldn't put a switch in for fuse 16, as it controls the entire Fan Control Module. When you pull fuse 16 it runs the fans because it knows that the FCM doesn't have power.

Some guys on the TDI forums have re-engineered a series of relays to imitate the operation of the FCM, but I can't speculate that it's a better solution than a properly working fan system. If everything is working now, don't try to change it; let the fans come on as they should, and keep an eye on your coolant levels.


As for me, I still have either a battery or a fan problem, but at least fuse 16 is staying solid, lol.

I got a new A/C Pressure switch in case that's the source of my problems, but I can't tell right now since the car doesn't have enough power to start . Voltage read 10.9V after the no-start, so I want to say it's the battery, but I'm going to take it to a mechanic for further investigation. As much as I like working on my cars, it's cold in Buffalo, and my truck has been in the garage for months, so I can't work on the TT in there.


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