2009 smart fortwo won't start

Hello Perked. The easiest thing is to start from the battery and work your way from there. Check the fuse marked F91 in the picture. If you have a multimeter or a 12 volt test light of some sort you can check to see if you have power on the wire AFTER the fuse. Set your multimeter on the 20 volt scale in order to read 12 volts on the car electrical system.Connect your meter or test light with the ground of the meter/light on the negative terminal at the battery. Then the positive wire to the battery plus lead and check for voltage. Then the wire right before the fuse and then after the fuse. A fully charged battery should be around 12.4 volts. Anything below 11 volts is for all intents and purposes dead. With the vehicle running and it charging you should get around 13.8 to 14.2 volts.

Maybe loosen up of the black ground battery cable and check it where it contacts the car (just above the F58 in the picture). The grounds are notorious for corroding and that could be your culprit. Next I would remove and clean the battery terminals and battery posts with sandpaper or a wire brush. DO this even if they don't appear dirty.
If that all checks out try putting jumper cables on it from another car or connect a battery charger and turn on the key and look for dash lights just to double check the condition of the battery. If jumper cables work or the battery charger causes you to have dash lights then you probably have a faulty battery or one that just needs recharged.

Worst case scenario is that you have a faulty computer on the car and it is called the SAM. It is the entire fuse box as a unit. It controls all the basic functions of the car on conjunction with the instrument cluster. Without the SAM working nothing on the car will do anything. It would take a long time to write all the reasons why you could have a dead Smart. But this should help you to begin troubleshooting. DCO

I am pretty sure that the switch itself is a typical on-off switch that opens or closes a contact to the SAM to tell the SAM to turn on. Once it turns on, the immobilizer ring around the switch reads your chip in your key and if the codes match the Sam goes ahead and cranks the engine over. The split second it starts to turn over you can release the key and the SAM will continue to roll the starter until the engine starts. When you first insert your key into the switch and turn it right over to start, you will notice that there is a short delay before the engine cranks. That is because the CANBUS is initializing. The Sam does most of the work but when it comes to CANBUS and the storing of error codes, that all happens in the instrument cluster. It stores info on the state of the CANBUS. But the cluster receives it's power from the SAM. The SAM is the central power to fire up all the modules and the instrument cluster. I think I would drop down the SAM or unplug the connectors and completely remove it. Open it up and look for corrosion or cold solder joints. The SAM boards are multi-layer so they are interconnected with ribbon cables, so there is a lot to check. There is a large red cable on the top side of the SAM that powers it from the battery. Check that connection and also read the voltage there to see of the SAM is actually receiving power. There are several relays inside the SAM that controls various things but I would just almost bet your power problem is inside the SAM. I have a PDF of the procedure for removing the SAM if you need it. Just PM me your emai address if you need it. I have more info I could probably conjure up. I have a lot of stuff archived on my laptop. Lastly do you have 4 way flashers that will turn on and flash? They will operate with the key off. So that should tell you if you are getting something from the battery. If you have the factory lowline radio (non CD and mp3 jack in the glove box) try the radio. It will operate 15 minutes before shutting itself down when the key is not on. So does that work also? You can remove the instrument cluster by grabbing both sides of it and gently pulling it towards you. Check those connections. If you have the Tach and clock pods those 3 wires run to the instrument cluster too. But check the connections. I have the pinout diagrams I think in a Microsoft Word format if you would need that. Last of all to check for power I would raise the car up in the rear and crawl under the driver side and remove that little cover that covers up the starter's solenoid and check for voltage there. If there is voltage bridge the battery terminal wire on the starter to the smaller wire and see if that activates the starter. DCO