Damn factory immobiliser

[tony_ack 0]

My factory immobiliser is playing up (surprise surprise).

 

I've had problems before, which I solved by wiggling a loose connection on the transponder box under the dash, and securing it better as the clip on one of the wires into it was broken. I then re-synced, and the car was fine.

 

Yesterday I went to start it (having only used it an hour previously) and the engine started, relay clicked, and engine cut out. I didn't have time to look at it further as I was late, so I took the missus' car instead. When I got back a few hours later I decided to have a look at it and re-sync again, but before I did that, I tried to start it. It started first time.

 

This morning, I went to start again, but the immobiliser was kicking in again. I had a little fiddle with the wiring into the transponder box, and re-synced for 10 minutes, but the immobiliser kicked in again. I had to take the missus' car to work and ended up being 30 minutes late - stupid thing.

 

Looking through past posts on the issue, there's quite a lot of conflicting information about how the system actually works.

 

As far as I can tell, there are several components in the system:

 

Transponder in key

Transponder reader

Transponder box

ECU

 

Again I'm not too sure about the specifics, but I guess that it works in the following way:

 

The transponder in the key is read by the ring and and sent to the transponder box under the dash which confirms the code. Once the code is confirmed a signal is sent to the ECU to allow continuous operation of the engine. I am guessing there is something in the ECU that makes the engine cut out if an OK signal is not received from the transponder.

 

The point of all this is I'm trying to work out where the problem lies. I would guess that there is either a problem with the connection to the transponder box, or the ring isn't reading correctly. I'm more inclined to believe it's the connection as I've had problems before, but I can't understand why it has been fine for 6 months, then failed on me for no reason last night (having driven the car fine all day), only for it to work again, and then fail again this morning.

 

Also, I'm not sure I understand the re-syncing process correctly - I was under the impression that every time there is a failed attempt to start due to the immobiliser, that you had to resync? Last time I had problems, the car wouldn't start until I resynced it. But then why did the car start okay last night after the earlier failed attempts, without a resync?

 

The other culprit could be the transponder ring - any guides for how to access/remove this for a clean and inspection?

[RW1 0]

Have you tried the tested method off WD40 soaking the transponder reader connection at the transponder box inside the dash?

 

If not, put some WD40 on the connection pins (3 pins/sockets). Gently side the connection a few times to remove corrossion. The WD40 will continue to seal afterwards.

 

There is no resync necessary.

 

All that will be reported in the diagnostics is code 17978 - "Engine Control Unit Blocked". This doesn't prevent an attempt to restart the engine again immediately if the ignition key transponder is able to handshake with the transponder box inside the dash.. The fault code can only be cleared using VCDS.

 

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[tony_ack 0]

WD40 is a good shout - I remember doing this last time when it failed in November.

 

Good to know that the resync isn't needed - does anyone know under what circumstances you do need to resync?

[RW1 0]

When you want to add a key or the immobiliser box or ECU is changed.

 

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[tony_ack 0]

Ah sorry, I may have been thinking of something else when I said 'resynching' - sorry for the confusion!

 

I was referring to the trick where you leave the key in the ignition for 10 minutes, with the ignition on before attempting another start. This seemed to work for me in the past where I cleaned up the contacts, and it still wouldn't start.

[RW1 0]

I was referring to the trick where you leave the key in the ignition for 10 minutes, with the ignition on before attempting another start.

 

Doesn't exist on the Corrado factory fit immobiliser. The immobiliser box just attempts to read the key's chip with the ignition barrel sensor ring each time a start is attempted.

 

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[tony_ack 0]

'Fixed' it yesterday.

 

Should be okay for another 6 months or so! It's a shame because the VW immobliser appears to be very effective. Just a little too effective sometimes.

[RW1 0]

Glad to hear!

 

WD40 I take it and bit of working the connection to push aside the corrosion?

 

Mine is usually good for about 7 years.

 

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[Declan Sedrick Lehane 10]

Holy thread revival, but where do I find the transponder box? I seem to have the exact same problem on my 95 VR - dumb question I am sure!

[seanl82 23]

Behind the dash, underneath the headlight switch and sits in the same bracket as the spoiler control module.

[Declan Sedrick Lehane 10]

How much of the dash do you need to take out, I guess start with the Fuse Cover Shelf, is it as simple as that or does more need to be removed!

[seanl82 23]

Take off the speedo binnacle and you should be able to get your hand in there. You'll be able to see it down by the light switch anyway.

[tony_ack 0]

Funny enough i came across this thread at the weekend as I was trying to find out how to recode a new ecu. It's a while since I looked at the transponder box but I'm pretty sure you can get to it fairly easily by just taking the lower dash shelf off on the driver side

 

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