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Recently my Smart 451, 2008 did not start. Turning the key into start position did not even turn the starter motor (no crank).

I am posting my experience and fix here hoping to help someone who's Smart car shows the same issues.

Notice and disclaimer: 1. Always disconnect the battery when doing work on the electrical system of the car. 2.I am not taking any responsible for what you are doing to your car. If you follow my test and repair instructions you do this at your own risk. Ask an expert if you are not sure about what you are doing.

Symptoms:

A) Turning the key into start position turns the lights on on the dashbard on but the P is not showing in the gear indicator area (see photo 1). Compare to photo 3 after fixing the problem where you can see the P in the proper place. Besides the dashboard lights turning on, a nervous beeping is also heard. Also the the dashboard lights are flashing, sometimes the key symbol shows, also the infamous three horizontal lines (bars) are flashing, but they do not stay on the display.
IMG_0548.JPG


Photo 1: Dashboard image with broken TCU

B) When I tried to use my scan tool it gave me an error message like "cannot connect to the OBD2 interface, please connect it, or something like that...) despite it was properly plugged into the OBD2 outlet of the smart.

C) When I disconnected the TCU (Transmission Control Unit ((module)) my scan tool was suddenly able to read error codes. Not for the TCU of course because it was not connected in that test. Make sure that you always properly disconnect and disconnect the battery before you properly disconnect and reconnect the TCU to avoid voltage spikes. You can possibly break parts of your on board computer-, sensor- and actuator- system in your smart if you do not do the disconnections and connections of the battery properly.

You find the TCU under the driver's seat underneath the carpet (see photo 2 for what the TCU looks like))

IMG_0578.JPG

Photo 2: This is how the TCU looks like. It is located under the driver's seat underneath the carpet.
To disconnect the plugs press on the plastic lever on the top of the connector and throw the U shaped plastic lever at the same time.

Repair:

Properly disconnect the battery.
Remove the driver;s seat (4 large torx screws)
Lift the carpet.
Disconnect the TCU wires and the brown ground cable.
Put in the replacement TCU and connect it correctly.
Put the seat back in.
Reconnect the battery.
When you try to start the car you may have to follow the the teach-in procedure for you smart's transmission (you may find that in your operator's manual under "Transmission").

IMG_0574.JPG

Photo 3: Dashboard image after replacement of the broken TCU. That is how it is supposed to look like.

I got a used TCU from ebay for about $200.

It takes about 30 minutes to replace the TCU

Good luck and I hope it works for you.
 

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Recently my Smart 451, 2008 did not start. Turning the key into start position did not even turn the starter motor (no crank).

I am posting my experience and fix here hoping to help someone who's Smart car shows the same issues.

Notice and disclaimer: 1. Always disconnect the battery when doing work on the electrical system of the car. 2.I am not taking any responsible for what you are doing to your car. If you follow my test and repair instructions you do this at your own risk. Ask an expert if you are not sure about what you are doing.

Symptoms:

A) Turning the key into start position turns the lights on on the dashbard on but the P is not showing in the gear indicator area (see photo 1). Compare to photo 3 after fixing the problem where you can see the P in the proper place. Besides the dashboard lights turning on, a nervous beeping is also heard. Also the the dashboard lights are flashing, sometimes the key symbol shows, also the infamous three horizontal lines (bars) are flashing, but they do not stay on the display.
View attachment 63899

Photo 1: Dashboard image with broken TCU

B) When I tried to use my scan tool it gave me an error message like "cannot connect to the OBD2 interface, please connect it, or something like that...) despite it was properly plugged into the OBD2 outlet of the smart.

C) When I disconnected the TCU (Transmission Control Unit ((module)) my scan tool was suddenly able to read error codes. Not for the TCU of course because it was not connected in that test. Make sure that you always properly disconnect and disconnect the battery before you properly disconnect and reconnect the TCU to avoid voltage spikes. You can possibly break parts of your on board computer-, sensor- and actuator- system in your smart if you do not do the disconnections and connections of the battery properly.

You find the TCU under the driver's seat underneath the carpet (see photo 2 for what the TCU looks like))

View attachment 63897
Photo 2: This is how the TCU looks like. It is located under the driver's seat underneath the carpet.
To disconnect the plugs press on the plastic lever on the top of the connector and throw the U shaped plastic lever at the same time.

Repair:

Properly disconnect the battery.
Remove the driver;s seat (4 large torx screws)
Lift the carpet.
Disconnect the TCU wires and the brown ground cable.
Put in the replacement TCU and connect it correctly.
Put the seat back in.
Reconnect the battery.
When you try to start the car you may have to follow the the teach-in procedure for you smart's transmission (you may find that in your operator's manual under "Transmission").

View attachment 63898
Photo 3: Dashboard image after replacement of the broken TCU. That is how it is supposed to look like.

I got a used TCU from ebay for about $200.

It takes about 30 minutes to replace the TCU

Good luck and I hope it works for you.
Hope you kept the old tcu. Do you know how to solder pc boards? My tcu and the mysterious SAM had intermittent problems, too. It stranded me many times. StealerMB wanted thousands to replace module(s) and I'm against wasting more money trying to fix my Smart Buying Error, a 2008 with all the software bug fixes I had to.pay for. So, I parked it until I cooled down. Then, I removed both modules and did the unthinkable. I TOOK THEM APART! The audacity of some owners. Unfolding the SAM boards, carefully and studying the solder joints, I found these things were soldered by an idiot! All but 3 joints between the boards and the pins out of the box were cold solder joints and cracked apart! Clean off the joints, desolder and resolder with silver solder and a good dose of flux and VOILA, both work great without opening my wallet for the usual fleecing.
Try it. It's electronics, not magic.
 

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Discussion Starter #5
Hope you kept the old tcu. Do you know how to solder pc boards? My tcu and the mysterious SAM had intermittent problems, too. It stranded me many times. StealerMB wanted thousands to replace module(s) and I'm against wasting more money trying to fix my Smart Buying Error, a 2008 with all the software bug fixes I had to.pay for. So, I parked it until I cooled down. Then, I removed both modules and did the unthinkable. I TOOK THEM APART! The audacity of some owners. Unfolding the SAM boards, carefully and studying the solder joints, I found these things were soldered by an idiot! All but 3 joints between the boards and the pins out of the box were cold solder joints and cracked apart! Clean off the joints, desolder and resolder with silver solder and a good dose of flux and VOILA, both work great without opening my wallet for the usual fleecing.
Try it. It's electronics, not magic.
Hi, Thanks for your hint.

I still do have my old TCU. I had opened it up as well but I could not find any bad contacts or shortened/ burned circuit parts on the board. I will recheck that.
 
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