Keyless Ignition and Immobiliser

[Kimble]

So, I bypassed the ignition key today and installed a protected starter switch.  All went well but it seems that I no longer need to use my immobiliser to start/drive the car.  It's as if I have successfully hot wired a car with an immobiliser.

I wired joined two connectors from the back of the ignition together and connected it to one of the switch points, the other one I just directly linked.

Does anyone have any ideas where I might have gone wrong?

 

[Jonathan Kay]

I think that we might need more details... which engine, which ECU, and which immobiliser? What are the colours of the wires at the ignition switch that you have connected? Can you add a sketch of the new wiring.

Is it possible that you've wired the ignition/ ECU so that it is never powered down in the way that it was?

Jonathan

[Kimble]

Sorry I should have provided more info, it's a 2004 K-Series R400 SV.  MBE ECU and what I guess is the standard immobiliser with little black key fob.  I ran the white & green line directly to the switch and merged the other two as per the diagrams I have seen.  I also have an FIA Isolator so a lot of the diagrams didn't seem to make sense.

From memory I think the other wires were brown and black but I can't be sure now.  I'll need to check tomorrow.

[revilla]

If we are talking about a Lucas 5AS immobiliser like this ...

... it should have a PERMANENT (i.e. still present when the ignition is switched off) +12V supply on a brown wire on pin 26 in addition to the ignition switched white wire on pin 1:

If this wire is either disconnected, or now switched with the ignition, the immobiliser will never arm itself.

This used to be a "cheap trick" to disable the immobiliser function, you just cut the brown wire.

When you turn the ignition off, the later models of the immobiliser passively arm; this relies on them counting for fixed countdown period, then arming the immobiliser if the ignition has remained off. So the immobiliser needs to remain powered to perform the countdown. If you take away the power when the ignition is off, it stops the clock, the immobiliser never gets to the end of its countdown and never arms itself.

It's worth checking whether that pin remains powered with the ignition off. It's an unsealed connector so you can just poke a multimeter probe into the back of the plug.

Note that this does mean that if the FIA switch is correctly wired, turning off the FIA key will also defeat the passive arming as it should remove all power from the immobiliser and so stop the clock.

[Kimble]

I managed to fix this by swapping the wires that go to the new ignition switch.  I was obviously bypassing the immobiliser.

I would love to spend a bit more time on the wiring and tidying it all up as it is quite confusing under the dash.  One day I will take the panel off and have a good inspection.

Suffice to say, this work and the echo location of the indicator buzzer whilst inverted in a tillet seat has taken it's toll on an already dodgy back!    

[7 wonders of the world]

converting your scuttle to be removable really is time well spent and very straight forward to..... saves you having to phone for help whilst stuck upside down in the footwell...