Smart Car Clutch Actuator and Gear Actuator Repair

Below: how the Smart gearbox uses its two actuators, the symptoms that point to each, why they wear out, and what happens once your garage sends one to us. Other automated manual gearboxes are covered across our clutch and gear actuator repairs.

What is the Smart automated manual gearbox, and which models have it?

The Smart gearbox is not a conventional automatic. It is an automated manual: a manual gearbox and clutch that the car operates for you. That is why there is no clutch pedal, and why you can switch between automatic and manual changes at the flick of a button.

Three parts share the work a driver’s left foot and left hand would normally do. The clutch actuator engages and releases the clutch, the gear shift actuator moves the gearbox from one gear to the next, and the gearbox ECU decides when each of them acts. Both actuators report their position back to the ECU, which weighs that against road speed and other inputs to pick the gear, time the next change and judge when to take up or release the clutch.

We repair these actuators from the Smart City, ForTwo, ForFour and Roadster; on the ForTwo, that takes in both the 450 and the 451 generations. If your Smart is not one of these, the part number on the unit is the quickest way to check, and we will confirm before anything is posted.

Smart car gearbox problems: the symptoms that point to an actuator

A failing actuator does not show itself the same way on every car. These are the four symptoms Smart owners bring to us most:

• Three bars or lines on the gear display. The bars appear where the gear number should be, and this is the sign we hear about most often.
• Slipping out of gear. A gear that was engaged lets go, and drive is lost.
• Stuck in neutral. The car will not take a gear, so it cannot move off.
• Failing to select gears. Changes are refused, or the gear asked for never arrives.

Left alone, any of these can end with a Smart that will not drive at all. When you fill in the repair form, tell us what the car was doing when the fault first appeared: pulling away, changing up on the move, or refusing a gear after being parked. That detail narrows the search before the unit is even on the bench. The wider picture across automated gearboxes is in our guide to clutch actuator fault symptoms.

Clutch actuator or gear actuator: which one has failed?

The gearbox ECU watches the two actuators separately, so its stored faults are the most reliable guide. Ask whoever reads the car to connect to the gearbox ECU itself, not only the engine, and to write down every code exactly as the tool displays it. Our guide to clutch actuator fault codes explains what the clutch-side and selector-side codes mean.

Symptoms on their own are less decisive. A Smart stuck in neutral may have a gear actuator that cannot move the gearbox, or a clutch actuator that never releases the clutch far enough for a gear to go in. Slipping out of gear and refused changes overlap in the same way, which is why we would rather see the codes than guess from how the car behaves.

If the codes still leave a doubt, send them to us before anything is removed. We will tell you whether to post the clutch actuator, the gear actuator, or both in one box.

What makes a Smart actuator fail?

Neither actuator gets a rest. Every pull-away, every change and every stop calls on one or both, and on a car built for town driving those demands pile up quickly. The causes we see sit at system level, and they often arrive together.

• Heat. The actuators are mounted on the gearbox, close to the engine, and go from cold to hot and back again on every journey.
• Town mileage. Queues and short trips add clutch engagements and gear changes far faster than open-road miles do.
• A wearing clutch. As the clutch wears, the clutch actuator has to travel further and work harder to do the same job, until the system can no longer make up the difference.
• Low battery voltage. Both actuators need a healthy supply to reach position on time. A weak battery or a poor earth can produce symptoms that look exactly like a failed unit, and both are quick to rule out.
• Contamination. Water, road salt and dirt at the connectors can upset the signals the gearbox ECU relies on.

The gearbox ECU can only act on what the actuators tell it. When a unit is slow to reach its position, or reports it inaccurately, the ECU plays safe: it refuses the change, holds neutral or stops selecting gears altogether. From the driver’s seat that feels like a broken gearbox, and it is how a Smart can be written off for a gearbox or clutch when one actuator was the real fault.

Why a replacement actuator is not the simple fix

Each Smart actuator is coded to its car. A new or used unit from anywhere else has to be coded before the gearbox ECU will work with it, so a straight swap is never just a part bolted on. A used actuator brings a further unknown: it has done the same job, through the same heat and the same traffic, as the one it replaces.

Repairing the original removes the coding question. Your actuator is already coded to your Smart and keeps that coding through our repair, so there is no coding step when it goes back on. Some cars do need the clutch touch-point recalibrated after the actuator is refitted. That follows from removing and refitting the unit at all, wherever it was repaired, and your garage handles it as a normal part of fitting.

That recalibration is also the straight answer for anyone searching for a way to reset a Smart clutch actuator. It is a fitting step your garage carries out with diagnostic equipment once a unit is on the car. It sets the gearbox up around a healthy actuator; it cannot bring a failing one back.

Diagnosis matters as much as the repair itself. A weak battery, a wiring fault and a worn clutch can each pass for a tired actuator, and a unit is only worth repairing once it has been shown to be the cause.

Smart clutch and gear actuator part numbers we see most

These are the Smart clutch and gear actuator part numbers that reach our workshop most often. Compare the number on your unit with the table.

The list is not complete. If your number is missing, send it to us and we will confirm we can help before you post anything.

How Sinspeed repairs your Smart actuator

Your garage keeps the car. We only need the actuator, sent by post to our Epsom workshop.

1. Codes and symptoms first

   Use the repair form to give us the registration, the model, every code from the gearbox ECU and a short account of what the car does. Tell us whether the box will hold the clutch actuator, the gear actuator or both.

2. Boxed up by your garage

   Removing a Smart actuator is normal workshop work for a garage. They protect the connector, pack the unit so it cannot shift in transit and post it to Epsom.

3. Measured on a simulated gearbox

   On our in-house Hardware-in-the-Loop rigs the actuator works against the heat, vibration and electrical load of a running Smart gearbox. We measure its movement and the position it reports, and keep it running until the fault you described shows itself.

4. Repair, calibration and a second full test

   Our engineers repair the unit in a cleanroom-standard, ESD-safe workshop and calibrate it with dealer-level diagnostic equipment. It then repeats the full rig test and is packed for return only when it passes.

5. Home to the same Smart

   Your garage refits the actuator, recalibrates the clutch touch-point if the car asks for it and clears the stored faults. Your unit keeps its coding, and the repair carries our lifetime warranty with no mileage limit.

We run the same service for Toyota MMT clutch and gear actuators and the Fiat and Alfa Dualogic clutch actuator, two more gearboxes that change gear without a clutch pedal.

Questions Smart owners ask