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I was lucky, I didn't have to replace any.
You could just measure them with ohm meter since they're close to a short it will be very obvious if it's blown open.
Good luck soldering, those thing are so small.
Cheers.
Question to Krakonosh and Bobby78.

My Kessy lost communication with the antennas long ago. So...

How to find out which resistors went kaput? Surely, the two transistors will have to be replaced, but there are quite a few resistors on that thing...

Thanks!

P.
 

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blown resistors

Thanks for the quick reply.

Now, I have to have those transistors shipped to Switzerland, as I have no idea where to find them here. Well, I'll package them with spark plugs because believe it or not, it is cheaper to buy spark plugs in the States and pay for shipping rather than buying them here. The prices here are simply insane and CHF is the most overpriced currency in the world. In real buying power 1 CHF= 0.6 USD, nevermind the official exchange rate.

I was lucky, I didn't have to replace any.
You could just measure them with ohm meter since they're close to a short it will be very obvious if it's blown open.
Good luck soldering, those thing are so small.
Cheers.
 

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ok i'm willing to take a look inside Kessy as I'm pretty handy with the soldering iron. My question is: Am I looking in the right place? It's never worked (as far as keyless entry) so I just assumed it was the antennas. Then one day I happened to grab the door handle with the key in my hand and poof door locked and unlocked when I tried again. I was stunned. of course, now it doesn't work again. ever once in awhile I get a "key battery dead" warning. So my question is... is it my FOB instead of kessy?
 

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I noticed my keyless entry is unreliable in cold weather, like below freezing. Also, I wore out one of the door buttons, the plastic spring no longer works (under the key cap). If I press that one while it's too cold, the other doors won't work. It seems like the worn out button jams the inputs for the other doors. In fact, sometimes the car won't lock as it will lock and immediately unlock. Very frustrating!
 

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ok i'm willing to take a look inside Kessy as I'm pretty handy with the soldering iron. My question is: Am I looking in the right place? It's never worked (as far as keyless entry) so I just assumed it was the antennas. Then one day I happened to grab the door handle with the key in my hand and poof door locked and unlocked when I tried again. I was stunned. of course, now it doesn't work again. ever once in awhile I get a "key battery dead" warning. So my question is... is it my FOB instead of kessy?
well, that's a $2 question. buy a new battery and you shall have your answer.
also, if you have a vagcom, the bad kessy shows up as bad antennas (all of them) on the scan.
 

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I noticed my keyless entry is unreliable in cold weather, like below freezing. Also, I wore out one of the door buttons, the plastic spring no longer works (under the key cap). If I press that one while it's too cold, the other doors won't work. It seems like the worn out button jams the inputs for the other doors. In fact, sometimes the car won't lock as it will lock and immediately unlock. Very frustrating!
you might be able to fix this problem by replacing the spring in the button. visit to a good indy shop.

actually, unless you replace the spring in the button, you are in it for a lot of $$$ if you want to get it fixed at your VW dealer. Check this out: I am almost certain they no longer carry "old-style" door handles, which means your fix will require a new handle, which has an updated antenna. But (!) the new handle will not work with the old Kessy. This means you have to replace all the handles and the Kessy... FYI, the replacement handles come unpainted from the factory and have to be painted to match your color ($$$ just keep adding up as we speak about the "proper" repair of your sticking door handle button at the dealer).
 

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Hi all,

Bobby78 has assisted my through testing my Kessy. I have completely tested all components in circuit around the 2 MOSFETS. apart from replacing the FETS, I have not been able to isolate the issue.

If there is a bad batch, can someone tell me the month and year the devices were in circuit that are bad.

Also, no one has actually worked out what the MOSFET's do, are they the pushpull drivers for low frequency proximity antennas?

For several weeks now, I have tried to reverse engineer kessy sections, and the MOSFET components section does not have anything to do with key not found, if anything, your keyless system operates around 400MHz, whereas the MOSFET circuit operates at much lower frequencies.

To-date I have not been able to find any functional description on the Kessy, obtain schematics, thus non the wiser. I am not prepared to spend big dollars, however I will replace the MOSFETS this week, cheap investment if they work.

If the replacement of MOSFETS fix my issue, we as a collective group need to provide feedback to VW and it is in their interest to properly diagnose Kessy issues and rectify design errors. :anger:

Regards


Gerald





Bad run of transistors? I think I've got a different problem as the LR door lock button stopped working after feeling like mush for a few weeks. The other handles worked fine until recently. Often as not now, if I get the other handles to lock the door the car unlocks immediately -- as thought the LR button is shorted out or stuck as, next morning, it works fine again (except for that particular handle).
 

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We have a few kessy modules about,
Mostly ones that we have replaced under warranty, sent back to germany, and they have denied the claim as the units are not faulty when tested at the hq labs.
Pm me with a part number and I will see what I can do.
 

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I took my kessy unit apart and identified the 2x mosfets and 6x resistors mentioned in this thread. I'm not sure on how to test these so I just ran a continuity test with a digital multimeter along each end of the components and found one of the mosfets with a short. All 6 resistors gave me continuity. Am I doing this the right way or do I need to de-solder the components in order to test them properly?

VCDS scan shows:

Address 05: Ace/Start Auth. Labels: 3D0-909-13x-05.1bl
Part No SW: 3DO 909135 M HW: 5WK470 26
Component: Kessy 6400
Coding: 0131304
Shop#: WSC 31414 000 00000
VCID:2F67FBD5C238
Part No: XXXXXXXXXXX
Component: EL V xxxx
5 Faults Found:
00179- Access/Start Authorization Antenna; Drivers Side (R134)
011 -Open Circuit
00180- Access/Start Authorization Antenna; Passenger Side (R135)
011 - Open Circuit
00181 -Access/Start Authorization Antenna (in Rear bumper) (R136)
011 - Open Circuit
00183- Interior Access/Start Authorization Antenna 1 (R138)
011 -Open Circuit
00576 - Terminal 15
009- Open or Short to Ground- Intermittent

I need help, thanks.
 

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Here is another success story of a kessy module coming back to life; Keyless (kessy) entry problem fixed ! after 5 dollars and 1 hour o - RennTech.org Forums

Of interest was the mention of;
"If kessy doesn't communicate with the scan tool, then it's the TWO MOSFET transistors that are fried.
If you have all antennas short to ground or not responding, then it's the 6 resistors."

In my case I get continuity across the resistors when I measure with a multimeter, however I have 4 Access/Start Authorization Antenna open circuit errors in VCDS?
 

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Update...I had one bad transistor on the Kessy module so I just replaced both transistors which are available for around $1 from here: IRFZ24NS FZ24NS HEXFET Power MOSFET International Rectifier: In Stock Buy Now | West Florida Components
Plugged the module back into the car, drove around a bit, and all doors+hatch came back to life. Also don't have the overnight battery dis-charge problem anymore.

Anybody with a non-working Kessy and battery dis-charge issue, I suggest you do this fix first before fiddling around with other probable causes to save yourself some valuable time and money.
 

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I may have time this weekend to replace both FETS.

I had the kessy replaced twice before under warrantee, each time it cost nearly AUD$500 + internal labour costs, $2 is not bad.

Regards

Gerald
 

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Interesting thread, I still have my old KESSY. For $5 in parts I am going to try rebuilding it. Once I've rebuilt it I should be able to put it back in the car to test correct? It was previously matched to the vehicle and both keys so my understanding is that it should still work? Definitely won't hurt to have a back-up KESSY where these seem to have such a high failure rate.
 

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Seeing how it's a spare module it should be less stressful doing the job. I was fretting that if I messed up with the soldering that I'd be unable to start the car anymore. There's quite a bit of solder on the back of the 2 transistors that holds them on the circuit board which requires a fare bit of heating to pry them off. De-solder the 2 pins from the board first then heat up the transistor until you feel it coming loose off the board. Once you replace them both, your keyless entry should magically jump back to life! Re-scan and you should not see any more "Access/Start Authorization Antenna" errors. A very satisfying DIY fix, so happy soldering.
 

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Took my old KESSY apart today and am trying to identify and test the components. In the first picture I believe these resistors to be the ones in question. In the second picture are the mosfets. So far I have continuity on the resistors, but haven't figured out how to test the mosfets with my multimeter. The issue with this KESSY is that the door handles wouldn't operate. Is it possible one of both of the mosfets could cause that? Resistors seem ok.



 

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I can't help much with testing the MOSFETs, not even sure if you can do that in the circuit. Just replace them, for the few bucks is a no brainer.
It worked for me.
I agree. Seeing how you're already in there just replace both transistors.
I had no continuity with one transistor which caused none of my door handles to function along with a parasitic battery drain.
 
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