Immobiliser issue after installing new battery.

[maxmc2]

Ill keep it brief, after installing a new battery the immobiliser now prevents the car from starting as confirmed in VAG-COM.

If i disconnect the battery and re-connect after a few mins the car starts and runs fine, turn off and then on again and its back to how it was before.

What part of the system could this be as its unlikely to be wires as it starts first time but not after that, could it be the receiver coil?

Any help would be appreciated before i start ripping things apart.

TIA

[itavaltalainen]

If you have VCDS then what fault code did it spit out?

[maxmc2]

The only code was that the engine start had been blocked by the immobiliser 17978, that was the only one.

[itavaltalainen]

In the ECU (controller 01) yes, but what bout immo controller (25)?

[maxmc2]

Nothing came up on the auto scan so guess i should select that controller in isolation? Can you still read measuring blocks on the free version?

Thanks.

[itavaltalainen]

Autoscan might not pick up immo box because not all had them.
Scan fault codes on it separately.

No idea if unregistered vcds lite does measuring blocks, I got the full whack.

[maxmc2]

Ok thanks ill try that tonight.

[danmusic24]

had the same thing years ago,all i done was used the key that goes into alarm thing under glove box and reset it!

[maxmc2]

I have now read the immobilisor and get this code

01177 - Engine Control Unit
           65-10 - Unathorized - Intermittent.

Any ideas?

[itavaltalainen]

How many keys do you have on your key chain?

Usually a faulty coil would cause a 'signal low' error code in the immo box. Unauthorised means that the read code does not match the IDs stored in the immobiliser. Maybe a dying transponder as well.

Get a second hand transponder and match all of yours to the immo box (you will need the login code from the black metal tag that came with the original keys).