I've been living with this problem for years.
My remote rarely, if ever, worked. I would have to hold the key close to the driver's door and pull on the handle repeatedly for the system to unlock the doors.
The right side antennas wouldn't recognize the key at all.
The most fun developed more recently where I would get into a back and forth battle of wills with the pig insisting on unlocking the doors after I locked them. I would have to try to hold the key just within range and then quickly move it away for the doors to stay locked.
Often this wouldn't even work so I would just leave the car unlocked (at work) or I discovered I could lock the doors with the transmitter near the right rear bumper after 3 or 4 tries. Very frustrating.
Never mind the fact that the remote didn't work from any remote distance at all.

So this thread saved me: https://www.clubtouareg.com/threads/....45716/page-12

I received the parts from digikey and gave it a go a few minutes ago.
So there are two MOSFETS and supposedly 6 resistors. My resistors were ok, and I think the premise behind them being a part of the equation is flawed... I'll get to that later.

The link has a good picture and description of where the module is and how to get it out, so I'll start from there with it out of the car.




Everyone likes a fun puzzle. I tried not to butcher it while cracking it open.


So you can use the diode checker function of your meter to test these, but I like to use just the ohm meter when I have a new part for comparison.
My MOSFET on the right checked out ok. You should read around 3 Megaohms across the two outer legs regardless of your probe polarity.
The one on the left measured around 10k.
You usually can't go by readings when a part is still in the circuit, but due to the symmetry of these circuits, I was hopeful that the 10k would remain across the transistor even with it removed.

I cut the two legs with small dikes and then used a regular soldering iron to heat up the heat sink (which is also the "drain"). I did this while gently prying it with a tiny screwdriver.
To get good thermal conductivity, you have to add some fresh solder to bridge the gap between the iron and the little bit of solder reachable at the edge.

Once removed, I was thrilled to find the 10k (bad) was still there.
I had to trim the heat sink. I used my large crimp tool cutters.
You also have to bend the legs of course. And trim the middle leg.





It's not exactly trivial to do this properly. I won't go too much into the details, but the correct way to do this would be with solder paste and a heat gun (surface mount rework tool).
But this is tricky since you can melt the stuff in the vicinity.
I tinned the bottom of the heat sink and heated up the pad real good, then positioned the part and tried to get a good connection as flush as I could.
Then (with the remnants of the cut legs removed) made sure I got a good joint on the gate and source.
Cleaned up with some alcohol and all done.


As far as those 6 resistors, You can see they are wired in parallel, which would not explain their use as protection fuses for the individual antenna legs.
For 0.22 ohms each, three in parallel would be (1/3 of one of them) around 0.07 ohms. This is pretty hard to measure with a regular meter.
Anyway since I don't think they're there for protection, and they measured about right (close to zero) I left them alone.


So that was it. It was a bit harder to get the bugger back in place but still cake.




These were the faults I had before attempting to reset. (There are two extra that were due to me disconnecting the module with the power still on so they don't count).




I reset and they did not come back.
I can't believe I have a car with a remote that works again!
The range is still beyond horrible, but I know that's just the way our pigs are. (Mine is a 2003 turbo.)
Oh yeah, the sneaky devil locked my keys in the car twice back when things weren't working. Once the key was even in the ignition and it locked me out!
Good thing I had AAA.

So here are the parts I ordered.
Might as well get the resistors just in case. But I wouldn't mess with them unless they're blown up or read open or something.


IRFZ24PBF
IRFZ24PBF-ND
MOSFET N-CH 60V 17A TO220AB

$6.32

SMM02040B2207JB300
749-1166-1-ND
RES 0.22 OHM 5% 1/4W MELF 0204

$2.48

EDIT:
This is the correct MOSFET:
IRFZ24SPBF-ND

Credit to theprf.

 

Great write up

 

Yes, this is excellent. My ‘06 turbo with entry and drive also acts like yours did (except my remote usually works). I’ve been meaning to pull my kessy and inspect. Glad to have your pictures and info!

 

That actual package for the fet appears to be a TO-263 D2PAK which would be an IRFZ24SPBF part.

 

Good deal. Makes sense. I added that info above.

While I'm here I wanted to add this text for people who may search in the future: 0179 0180 0181 key not found KESSY

 

Update:

So everything worked for I think it was 2 days. Then it started to fail in two stages.

First it would do the thing where it would insist on re-unlocking every time I tried to lock and walk away.
While it was in this stage, it only showed the rear bumper antennas as faulty.
(I remember years ago when the problem first started, it was only the rear antenna fault that kept coming back initially.)

Within a day or two everything returned to square one, with all of the exterior antennas showing open and no range on the key remote.

To my surprise the right side MOSFET went bad this time (measured 1,000 ohms from gate to source).

Well I had a few extra still so this time even though the left one still read good I replaced them both.
I learned about "matched pairs" of transistors when I was a kid and it looks like these two do work together... I guess a push-pull affair.
Anyway I'm glad I got a second crack at it because I saw my first replacement wasn't down flush with the board. Getting the correct transistors with the pre-bent leads would have helped with this.

I also remembered I had a better tip for my Weller.

This is an 800 degree wedge tip and made quick work of the job. Sooo much easier.

But before replacing the transistors I ordered a used rear bumper antenna from eBay for $12.
After getting the bumper off I measured both of my antennas. The left one (that I suspected) measured 10 ohms and the right one measured 4, the same as the eBay one.
I would have thought that the bad antenna would have measured lower, but my results jived with one other person's experience from a Touareg board.






After doing the job, the remote didn't work actually. Or it would work once in a blue moon.
I was sad for a day or two until I remembered that for the brief time I had things working, the green light on the remote would light up (something I never noticed before strangely) but now it wasn't lighting at all (new battery).
Then I confirmed that the times I could get the remote to work, the green LED would light.

I had a Chinese knockoff remote key that I had planned on trying to con a dealer into programming (but never did) so I swapped the guts of my key and sure enough it was just the button not working.
It works now every time and is fixed again like the first time.
It's been 5 days and it's still working.


So now the variables are, was it the mis-matched transistors or the bumper antenna or both?
And how much did my non-functional remote play a role? Sorry it's not so cut and dry... probably a combination of everything.

Oh and to make things worse, I never mentioned the thumb buttons to lock on the door handles still don't work.
But it looks like this is a separate issue. I think it may be one of them is shorted.
I ordered one from a junkyard yesterday.


I have a hunch the problem is the left rear, as it's been acting strange lately. Someone else here has the same issue where it sometimes tries to lock itself 3 times in a row instead of just once.
And before the repair, occasionally the same door would remain unlocked after securing the alarm.
Maybe this is a micro-switch issue I've heard of though...(?)
I'll report back if/when I ever fix the lock with your thumb problem. Not a big deal though as long as the MOSFET repair holds and I can use my remote.

 

Good info. thanks for the post. I did the solder job once in 2014 and again in 2024. I replaced mosfets and resisters both times. But as you said, I could never tell if the resistors were bad. I think it was the mosfets both times they failed, which seems to be once every ten years.

I also recently had my rear hatch stop unlocking using the keyless system. It would only work with the remote. I replaced both rear antenna’s under the bumper with new ones. They were $37 each. All good now.

 

Good to hear, thanks!
To further complicate things, it seems the transistors in later modules are replaced with BUK7635-55A which are rated at twice the current.
And as a side point, I haven't done the research to determine for sure, but it could be in these later units, the resistors may be different. In either case, I noticed mine are orange, orange, silver so .33 ohms not .22.
Just reason enough for me to continue with the original transistors.
The bigger reason though (to me) is, I'd much rather replace the transistors that seem to go very peacefully in their sleep, than have to touch those tiny resistors or something else that would be taken out violently with twice the current.
Oh I forgot to mention, if the MOSFETs do go again, I'm replacing the three blue rectangular caps. I found them online and understand that when switching amplifiers fail, in general the cause is often the capacitors.
Hopefully my repair will hold at least 10 years as well.

 

Good info, again! My car also has partially working lock buttons on the handles (I think 3/4 or 2/4 work usually). Also, I can’t unlock by placing my hand on the handle. I have to pull it a few times and then it will unlock. Is that an issue with your car as well?

 

If I recall correctly, I always have to give a first futile pull before the doors unlock, but at least now all four doors will open this way.
I know I'm getting warmer, but still have some problems. The good thing is, no faults have returned and my remote still works.

I found an FCC test document that explains the system (sort of). It looks like the multiple exterior antennas (and some interior ones) actually broadcast pulses out at 125 kHz.
The pulses try to sense the presence of the key.
And I think the remote unlock button is separate and operates at 315 MHz.
I'm not sure if anyone has seen these documents, but it's pretty cool stuff. I think we can figure it out.

https://fcc.report/FCC-ID/KR5KESSY

Forgot to mention, so there's only one transmitter circuit (the FETs and transformer) and the six relays quickly switch between the six antenna groups for the pulses.
It's cool how you can hear them quickly pulse in the initialization sequence that happens when you connect up to the KESSY. I use iCarSoft.
It sounds like quickly rapping your fingers on a table cyclically like you were practicing for piano or something.

 

I did this exact same thing last year and went through all of these same steps. Unfortunately for me, like many others have also said, the problems reared their ugly heads again. Usually another issue is causing the resistors and MOSFETs to blow. Without addressing that underlying issue, the gremlins inevitably always pop back up. With that said, I hope it's different for you (I didn't address my antennae), so please definitely report back if things remain fixed for the long haul - that would be awesome.

 

Yeah I think the issue was the antenna.
My first engineering assignment was as an RF engineer actually. I never became an expert, but I learned about the importance of impedance matching.
So with the one antenna being out of whack I think the energy sent out to broadcast gets reflected back to the source and damages the mosfets.
I'll definitely report back if it fails again.

I'm also getting warmer with my thumb button push to lock issue.
I found a post where a guy explains that there are some splices on the right side of the car, back further, that I may have missed.
These screw up the function of the rear comfort module. I occasionally lose all communication to that module until I reset it. The symptoms sound like my issue.
Here is that link. The English is not so good, but it's great info.
https://rennlist.com/forums/cayenne-...oth-sides.html

Does anyone know if iCarSoft can talk to the rear door modules? I can't with mine. Can't talk to my seat memory modules either.

 

Good to know.

The KESSY swaps fixed all my thumb button and keyless entry issues. I can't offer much help here, but if one system is out of whack on the CAN-Comfort then the whole system tends to fault. Look at the wiring diagrams and try and identify an area where all of your issues seems to converge. For me, every fault centered around, or involved, the rear comfort control module. Turns out I had a faulty unit which in turn shut down other items which relied upon the unit. You could have a bad ground that needs cleaning, or a loose splice, but definitely give the diagrams a look.

I have the new iCarSoft 3. I haven't tried talking to the door modules, but my gut says it can't. When I get some time I'll try and check for you.

 

Mine is kinda weird, as I have similar symptoms but no fault codes. I’m hoping an easy to find bad splice or a dying mosfet is the culprit, but it’s harder to pinpoint without a fault code.

 

I never had any luck diagnosing with Durametric. I replaced the mosfets based on what I read on the forums. It worked. This time round I also replaced the rear antennas as my rear hatch had stopped working after I refreshed the mosfets. I subscribe to the phylosophy that the more components that are failed the more out of whack the system(s) get. So I try and stay on top of it. Replacing the fets and the antennas has the system working again. Both my rear door handles unlock ok, but don’t lock. That is a persistent 15 year old problem. I’ll work on that next.