SAM Unit (Fuse Box)

Mod Description

It's a name that gets banded around especially by Roadster owners but not that many people actually know what it is, even less know what's inside.

Mod Details

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So What Is The SAM Unit?

Essentially it is a fuse box with internal relays and a microprocessor that controls almost all of the electrical functions of the car. The processor is flashable so it can be taught new tricks by way of a TAN code, these tricks include paddle gear shift, auto door locking, automatic gear change, day time running lights, cruise control etc.

What Does SAM Stand For?

Signal Acquisition & Actuation Module.

Where Is It?

It can be found at the top of the footwell, passenger side of a RHD smart city coupe/cabrio, drivers side of a LHD smart city coupe/cabrio and the drivers side of a Roadster.

What Does It Look Like?

Just a plain boring black box with fuses pushed into the front. Although the SAM units all look the same, the new 452 internals are slightly different.

What About The Bits We Can’t See?

The top side is where most of the wiring goes to, there are 10 connections and a positive input. All inputs are labled. Each circuit has its own earth point around the car.

There Is Something Missing

Damn right, Relays. Most cars have relays in the fuse box, these control the horn, wipers, indicators, lights etc. The relays visible on the smart are for the fog light and heated seats.

How Does That Work Then?

No different except in this case the relays are actually inside the SAM unit.

Inside The SAM Unit

Remove the three Torx10 screws.

Unclip all the plastic clips around the outside

With the top off you see the main fuse connections

With it removed from the box you see the relays and connectors

The board is in 4 parts and is bent around on itself, you can see the cracks between the tracks but this is normal. The tracks are OK.

PCB 1, 2 and 3 fold open and a flat plastic retainer can be removed

PCB 2 is populated with the microprocessor and many small relays

This shows the main functions of the relays on PCB 1

This shows the single relay on the back of PCB 3

And there are 2 relays over on PCB 4.

What Do The Relays Power?

Work in progress

No User Servicable Parts Inside

You can say that again, if you get water in this there is nothing that can be done. There is nothing you can take out or change, everything is soldered directly to the PCBs.

What About Microchips?

There are surprisingly few IC packages inside the SAM unit. The main one however is the Motorola MC9S12DG256C which is a 112 pin 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit (HCS12 CPU), 256K bytes of Flash  EEPROM and a whole load of other stuff that means very little to me.

If you want to know more about this chip. Click here.

SAM connections

700cc Fortwo And Roadster