immobilizer on 96 EU models

[Clemens]

I know, most of you haven't had an EU 96 model with the chipped key and immobilizer.

But since in Germany there seems to be some kinda Muerta about immobilizers (because it is illegal to talk about disabling the anti theft mechanism on a 26 year old car), I am trying to gather as much information as possible.

As I believe the VIN is scripted into the ECU from 99 onwards because ECU tuners need the original ECU for upgrades or clones of 99+ ECUs.
When I had a spare ECU reflashed recently the guy who did it (well respected Volvo tuner in German fora) did some magic to accept the immobilizer, but refused to remove the immobilizer completely.

I think that the chip and antenna ring must match each other.
I know that you can mount the chipped key near the antenna ring permanently. this has been done.
I know that the alarm system can be disabled by bridging the relay. I had to do this when my FOB failed and I barely made it home in the middle of the night.
The alarm system is not connected to the immobilizer, it simply cuts the ignition or sthg. similar. After years with the bridged relay I feel safe to say this is a permanent fix.
I know that you can't acces the ECU by OBD 2 if the antenna and chip don't match.

What I don't know is:
Does the antenna ring decode the signal or is there a decoder that sends the signal to the ECU?
And is the signal semt simply a "Go ECU" or does it communicate back to the chip decoder?

The reason I want to know all that is not because I want to steal my own 96 R but because I'm trying to be prepared if electronic gremlins arrive.
Can a chip and antenna ring be replaced as a set or is there a controller box that would need to be replaced as well? Or is the chip controller box (if there is one) matched to the ECU?

[abscate]

I’ve swapped antenna rings on 1999 models without affecting function. It is just an antenna without any software or any other hardware , except a light.

[scot850]

On the 99-00 models over here, the antenna is purely a code reader. You can swap these without concern or any re-programming worries. I don't believe the Euro spec ones would be anything different.

Our friend Xanethin has a good deal on knowledge on the systems and there is info on this thread I started a couple of weeks ago:

viewtopic.php?t=101018

Neil.

[misha]

Untill s,v70 hit the EU market in '97....850s need immo box (with same part # as old one)with matching chipped keys.
Ecu isn't coded but it will seek for "green light" from immo box.

Chipped key transfers a code via antenna ring and sends it to immo box.
Then...immo box sends "green light" to ecu.

Immo box MUST be replaced with matching chipped keys and MUST have the same part # as old immo box.
Antenna ring is there just to transfer a code from a chipped key to immo box.

S,v70 from '97-'99 needs immo box with matching chipped keys AND matching ecu.

[Goupil]

The immobilizer module Misha is talking about looks like this
https://www.ebay.co.uk/itm/224173405239
And should be situated near the steering shaft, under the dash. The volvo schematics says on the right of it for a 96 850.

Worst case if you have immo problems and the ecu is M4.4, you can flash a north american market map and the car will start even without a signal from the immo..

[Clemens]

Thank you, gentlemen, that helps alot

[scot850]

Removed content as in wrong thread.

[Clemens]

Have you checked the thermostat? When was it last changed?

Neil.

Neil, I think this post was supposed to go somewhere else. If not, please further exlplain what you mean.

[scot850]

?Um yes it was meant to go somewhere else. Clearly I have been stupid and somehow attached to the wrong thread! Ooops!

Neil.