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Interior guides and mods

450 Child Seat Frame

Modification Details

Baby Seat Fixing

Did you decide to bring a noisy, life sucking, pooing and spewing, useless meat bag into this world?
Did you think that keeping your smart was a good idea?

If you answered yes to both of these, there is something mentally wrong with you.

However, after going through months of discomfort and the pain of child birth, the last thing you want is to watch
your beloved meat bag shoot out the windscreen or turn into pâté when the airbag goes off when you crash.

Good News!

Smart do a special fixing that bolts under the passenger seat that allows you to attach a
baby seat securely and it also diasbles the airbag on that side when the seat is installed.

Smart part number Q0001848V010000000

Ask at a local smart dealer. If they have discontinued it, search on eBay for the part number.


This is the kit. It consists of the main fixing bar, 2 bolts and 2 collars.
The right hand end has a black plastic box on it. This contains the switch that deactivates the airbag.

On each end is a plate. These rotate for reasons that will become apparent later on.
The plate on the right end spins all the way around but the left hand end is limited.
Rotate the left end plate anticlockwise until it hits the stop.

Fold the passenger seat forward to give you a bit more space to work. Slide the seat forward as well.
Push the fixing bar into the back of the seat base. Notice that each plate has a threaded nut welded on it.

These are the fixings.

Take the collar and push it into the middle hole on the outside of the seat base...

...and push one of the bolts into the middle of the collar.

Move the end plate around until the bolt can pass into the threaded nut. Tighten the bolt finger tight.
Push the back of the plate downwards so it rotates anticlockwise... this allows the plate to make contact with part of the seat base.

Tighten the bolt up fully using a Torx45 bit. Do it up tight.

Move over to the other end and, as before, put the collar into the centre hole.

Place the bolt into the hole in the collar.

Line up the plate so the bolt can pass into the threaded nut on the plate.
Push the plate downwards so it rotates clockwise and touches part of the seat base.

Tighten this end's bolt with the Torx45 bit again. Do it up tight.

The bracket is now correctly fitted.


Under the passenger seat carpet should be a connector with 2 wires (although the connector has 3 holes).
It's easier to remove the seat to find the connector but it's not impossible to do with the seat in place.

Plug it into the connector coming off of the baby seat fixing.

That's the wiring done. How you route the wire is up to you.


If you plug the seat base in but don't have the car coded, the airbag light will come on and stay on.
This is bad, you don't want this. If the light comes on like this, none of the airbags will work.

If you have an MB Star machine you can do this yourself. If you
don't, a smart dealer or smart specialist wil do the following steps.

Identify car by VIN.
Control unit adaption.
Activate child seat lock recognition.

Now when you turn the car on, the airbag light will come on for a few seconds and go off as normal.

When you have the child seat fitted, the airbag light will flash for 15 seconds before going out.

Using The Seat Fixing Base

The fixing base can be swivelled out of the way when not in use.

Fold the seat down...

...and twist the seat base forward on top of the seat base.

Fold the seat back up again and you'll see the fixings protruding between the seat base and backrest.

You can not clip your seat onto the base. Put a towel down on teh seat base to protect it from the baby seat.

How It Works

It's a very simple system. On one of the metal loops, you'll notice a black box with a cable coming from it.

The box contains a small PCB and a switch. It's held on with 4 small screws.

Once removed, there is a single posi screw in the back.

With the posi screw out, you can remove the lid and see the PCB and switch.

The PCB is a simple thing. Depending on the position of the switch, the connection is either through...

...the 150 Ohm resistor on its own or both the 249 Ohm and the 150 Ohm resistors (total of 399 Ohms).

With the baby seat not fitted, you get the (approximate) 399 Ohms.

With the baby seat fitted (which presses in the switch) you get the (approximately) 150 Ohm reading.

Can I Make My Own Switch?

Yes, if you have a different baby seat and want to turn the passenger airbags off, you can make a simple switch.
You could copy the original layout or use a 150 Ohm and a 400 Ohm.

Is The Smart Seat Fixing ISOFIX Compatible?

No, it's not. Here is the ISOfix standard sizing.

But this is what the smart fixing system has.

So, the bad news is that you are somewhat limited to smart's seat and base.

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