453 – 3 Lines On The Speedo

3 Lines, 3 Dashes, 3 Bars

Like all previous smart models, the car will show 3 lines on the speedometer if there’s a transmission fault.

On the 453, this should only ever be possible on the 6 speed DCT “auto” gearbox because the manual gearbox is dumb as a bag of gears and the EQ has a single ratio.

Initially, the screen should also show “Gearbox fault. Go to workshop”. Unless you don’t have an English car…

It’s French so probably something about going on strike and setting stuff on fire.

Things To Check

Fuses

Front Fuse Box F1 – Fuse 6 (50amp)
Interior Fuse Box F2 – Fuse 45 (5amp) & Fuse 15 (5amp) – Use the handbook layout.
Rear Fuse Box F11 – Fuse 8 (10amp)

The list of fuse locations can be found here.

Weak Battery

The 453 DCT is complicated and takes a lot of power to move everything into position at a fast enough rate to keep the car happy. A 12v battery with low current can slow the system down enough that the car could panic. Checking the voltage just isn’t enough and we know from experience that the 453 battery is cheap and poor quality. The start/stop system and excessive charging current kills them in short order.

It’s possible for a battery to show the correct voltage but not output nearly enough amperage. The 453 is a bit of a diva when it doesn’t get the current it wants.

Don’t go and buy a new battery straight away. Try a set of jump leads and another battery to boost what you already have. It’ll be a janky setup but if you remove the bonnet, place the 2nd battery in the passenger footwell and run the jump leads through the open passenger window, you should be able to drive it enough to determine whether it’s the battery at fault.

Also, it’s worth cleaning and checking the tightness of the battery terminals and the battery to body earth cable tightness.

Alignment

Much like the previous models, it is possible for the clutch actuator or gear motor to become misaligned. Depending on the reason this happened, it might be a simple fix by reseting the position back to the car using MB Star.

Brake Lights

When you press the brake pedal, do the brake lights come on? If not, check the brake light switch. It’s part of the ESP circuit and connected to the transmission controller which obviously controls the transmission.

Transmission Controller

Unlike the gearbox controller on the 451, the 453 has it on the outside of the cabin. Unless you’ve run yourself over with the car, there’s a good chance you haven’t seen it as it’s bolted to the side of the gearbox itself.

If you can send me a better photograph of this unit, that’d be great.

It’s a bit early to start saying that these will fail just because they are French electrics but I think we can safely presume they’ll be a problem at some point.

Selector Lever Module

It’s unlikely to be the issue but it’s worth noting that the gear lever is wired to the clutch transmission control unit so a failure inside the unit could send erroneous signals that may confuse the controller.

Earth Points

Smart label it as W49 – transmission ground point. So it’ll be in the engine bay somewhere. You’ll probably have to wear the car like a hat to find it though.

Gearbox Fluid

There have been people who have suffered extensive gearbox fluid loss, causing the gearbox to seize. Most of these people were towing their 453 in “tow mode” and somehow the car jumped out of neutral and span the gearbox up. The seals fail and it dumps the gearbox fluid into the bell housing.

Checking the level isn’t easy. It’s generally better to just do a fluid change and inspect the removed fluid (if there is any).

Electrical Connections

At the end of every wire is a connector of some type. It’s not unusual for there to be connection issues (see French electrics).
There are 2 electrical connectors to the transmission controller, however, 1 of those connectors leads on to 2 more connectors before the wires reach their destination.

X26 sits between the transmission controller and the fusebox F1 and fusebox F2.
X25 sits between the transmission controller the gear selector module, steering wheel clock spring, fusebox F11, fusebox F2, SAM-M,

SAM-M

The 2 SAM units on the 453 are going to be a big future fault. I’m hearing a lot of SAM-M and SAM-D units failing. Not full failure, they just generally stop controlling 1 or 2 things like the wipers not working, headlights not turning off, brake lights not turning on etc. Every few months I hear of another circuit that was affected by a failed SAM unit. Although I’ve not experienced a transmission fault because of the SAM-M but it does send stop lamp switch position information to the transmission controller, so there’s always a small possibility.

Damaged Wires

On previous models, the wires were prone to rubbing through and short circuiting. It’s a bit early in the car’s lifetime to expect that to be happening but that doesn’t mean that external factors haven’t damaged wires.

Failure Of Parts

Don’t start throwing parts at the car. MB Star Xentry should be able to narrow down the exact faulty part but it could be 1 of the 2 clutch motors, the gear position motors, 1 of the 2 transmission RPM sensors, transmission mode recognition sensor, SAM-M unit, ECU, brake lamp switch

Anything Else?

All of what is above is from the top of my head after looking at the wiring diagrams. If I think of anything else, I’ll add it. If you think of anything else, let me know and I’ll consider adding it.

Credits

Thanks to Fab for the photos of the speedo.