smart car specialist

Smart Frequently Asked Question

Quick Links	Model type
Air con Roadster	452
Airbag light	450/451/452
Brakes	450/451/452
Door handle	450
Dump Valves	450/452/451
Engine	450/452
Engine light	450/451/452
Fuel and Oil	450/452
Funny noise at the front	450/452
Gearbox	450/452
Handbrake	450/451/452
Headlight bulb	450/451
Headlights	450
Heater fan For Two	450
Heater fan Roadster	452
Keys	450/451/452/454
Lack of power	450/452
Oil usage	450/452
Roadster interior door handle	452
Steering	450/452
Steering Wheel	450/451/452
Turbo	450/452
Turbo noise	450/452
Valve Burnt out	450/452
Safety Note	450/451/452/454

Q The air conditioning in my roadster is not working, why?	452
A Most likely it’s the Alloy pipe that connects to the air conditioning compressor in the engine bay, the early design was prone to fracture, there is a modified suction pipe now with more flexible coupling.

Q My airbag light has come on do I need to worry?	450/451/452
A Yes, usually if the light is on the unit will default to non function. If you have side airbags moving the seat can cause the light to come on the cables are secured under the seat and moving it or putting items under the seat can disturb the wiring. Get it checked out on a Smart specific diagnostics machine

Q When driving slowly I get a weird spring sensation through the brake pedal and a noise to accompany it?	450/451/452
A Get someone to check the ABS Reluctor rings (they are at the end of each rear driveshaft), these corrode and split over a period of time making the abs not work when it should be, the split rings give incorrect signals to the ABS sensors that in turn makes the abs pump unit work when it is not required. Get new driveshaft's or have a qualified person replace the abs timing rings. Safety note; the abs and ESP may not work properly in an emergency if these are faulty.

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Q My 42 door handle was stiff and now I cant get in, is this just the cable?	450
A Its probably the exterior handle, the cable has to make a tight turn inside the door and cable suffers and becomes stiff and finally breaks. A new Bowden cable is usually required.

Q I have heard dump valves are good on turbo engines, can I fit one to my Smart?	450/452/451
A No, it is not recommended, there is a formula for determining the size of the aperture in the dump valve and most dump valves simply dump too much boost for the smart meaning instead of preventing the turbo 'stalling' (stopping as boost backs up in the system as the throttle is shut) , it dumps too much boost causing the turbo to over speed risking damaging the turbo bearings, most expel oil also causing the engine bay to be covered in an oily film also.
Nb. Brabus Smarts do not have a dump valve fitted and BRABUS did have a car in the Guinness book of records as the fastest 4 door car in the world at 212mph so they know a bit about tuning.

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Q Why are these engines so weak? Why are they be worn out so quickly?	450/452
A Well firstly lets get this into perspective a 61bhp 599cc car is making 101.83 Bhp per litre, very impressive that’s the same specific power output as an E36 BMW M3. All from that little engine with only 2.7 litres of oil to cool and lubricate it. Most are driven flat out, full throttle everywhere, often poor maintenance, sometimes only 3 spark plugs have been changed (they have 6: two per cylinder) and the wrong oil, low grade fuel. There are many running high mileages and achieving 55+mpg, they do get a gentler life. Smart state in the handbook "Normal operation at constant speed 2000-3000rpm, brief periods of acceleration, e.g. when passing 3000-6300rpm"

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Q I have a performance exhaust and my engine light has come on, is the exhaust faulty?	450/451/452
A No not necessarily, the smart car has set parameters for all the engines settings, by changing them from standard you run the risk of the engine management unit thinking there is a problem. Changing any part of the car can cause this but exhausts and air filters are most common.
NB. You can buy a unit that fits between the exhaust and lambda sensor that alters the reading reducing the chance of the engine light coming on.

Q I heard a funny 'TWANG' noise from the front of my car, do I need to worry?	450/452
A Yes as the noise could be the top of one of the front coil springs shearing, did you find a inch long piece of black/rusty semi circular metal nearby?
2. The front end suffers all the crashes and bangs you too feel from the cars suspension. The springs seems to rub in the top cup causing damage just as it locates in the top cup, over a period of time this gets worse and one day the spring shears off. NB always get both done always and change the top mounts as the design has been changed.
NB. Usually replaced in pairs

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Q Why is the correct oil and fuel and plugs are so important?	450/452
A Oil 0w – 40w (UK spec) Fully Synthetic, Mobil 1 is recommended in the Smart handbook up until about 2004 (We have tried other oils but the smart does not like them, it burns them differently and quickly! ) and can cause the carbon build up or increased wear.
NB. The Smart turbocharged engine also puts special requirements on fuel. Turbochargers make more power, in doing so increase the temperatures the engine has to deal with. The inclusion of oil left in the combustion chamber means the oil is burnt and the oil burns at higher temperature causing increased heat inside the engine and the oil residue leaves a carbon coating that builds up over time.
Higher octane fuel RESISTS detonation better so the engine can run closer to its limits for making decent power without having to ‘back off’ to preserve the engine. BRABUS models are meant to use only 98+ Ron fuel (indicated in the fuel filler flap) There are additional cleaning additives used in premium fuels but we do not have test data to prove or disprove the usefulness in Smart applications.
NB Spark plugs must be changed as per the service schedule, failure to do so will could mean pre ignition (see above) or plug failure or destruction, any of which could mean engine failure

Q Why is my car is having trouble selecting gear?	450/452
A It could be one of several things
1. Check the rear lights to see if the brake lights are working if not then its probably the brake light switch faulty and need replacing, its between the under tray and the car chassis and really need the car on a ramp
2. Then the wiring to the gear selector motor need to be checked to see if the intercooler shroud is chaffing the wiring causing electrical short circuits, if so the wiring need to be cut and rejoined and the intercooler shroud modified so it wont damage the wire again
3. Check the clutch actuator adjustment and operation
4. The clutch unit may be worn and need replacing, always replace the release bearing at the same time.
5. 451 Models we suggest getting the get the software updated at a Mercedes main dealer, if this does not cure it then you may need a new pressure and friction plate (complete clutch module)	451
Q My handbrake travel is very high?	450/451/452
A Its probably the rear shoes and adjusters need cleaning and adjusting properly, these usually get done about every 4th year - it could be the rear wheel cylinder seals have failed and are weeping brake fluid, a competent garage can remove the rear hubs and clean and inspect the cylinders and replace and adjust as necessary

Q My headlight bulbs have gone again is there an easy way to do it myself?	450/451
A No, either you have the skill or you don’t, if you try and accidently dislodge the spring clip the headlight has to be removed and the front end will have to come off to replace it and then the headlight need re aligning too.
2. Go to a Smart specialist garage who have experience in doing it.
3 451 Model yes, refer to your handbook for how to change the headlight bulb,

Q My 42 headlights make a funny noise?	450
A its probably the headlight adjustment motor, they can fail and the noise you hear is them perpetually adjusting, replacement or disconnect and correct setup on a MOT alignment unit are the alternatives

Q The heating fan in my 42 only works on full why?	450
A The resistor is faulty and need replacing, its a simple job and not too costly

Q The heating fan in my roadster is not working, why?	452
A Most likely it’s the connection to the switch itself, they seem to have a poor connection there and the connection arcs and burns away the metal in the switch unit. It needs repairing, sometimes a piece of wiring loom and connector are required and sometimes the central consol unit will also need to be replaced

Q My key wont unlock the car is it the battery in the key fob low?	450/451/452/454
A it could be, more likely the key has lost is coding and will have to be re coded along with the car and any spare keys you might have too.
If the battery is low the indicators will flash 9 times quickly (indicating you can use it 100 times more - so change the battery asap)
Batteries are as follows - see the handbook for how to.
450 City Coupe 600cc 1 button key CR2016
450 Crossblade CR1225
450 Fortwo 599cc CR1225
450 Fortwo 698cc CR1225
450 Fortwo 799cc early CDI Diesel 1998-2007) CR1225
451 Fortwo 999cc (71/84bhp) CR2016
452 Roadster CR1225
454 Forfour CR2016

Nb When changing batteries observe correct polarity and change them promptly - Batteries available in many retail outlets/Garages.
NB Try to use both keys equally and often. There has been no satisfactory explanation as to why they lose the programming

Q My Car is going very slow like its got no turbo boost?	450/452
A Ok 1.first thing to check is under the rear of the car the waste gate arm, its held in place by a tiny E clip and these can rust and fall off, no boost will be allowed at this point, be careful as the exhaust is very hot and you need a clip to be able to fix it.
2. If the car is standard get the car diagnostics checked, it could be the cycle valve, check the hoses to it and if need be change the cycle valve unit (its reading determine if boost is produced or not) then check the boost pressure sensor, or in the case of remapped cars it could have gone into safe mode (a get you home mode much less power) if you have a high power map and had all the electrics on and air con putting the engine under more load, making it work closer to it maximum boost level.

Q My car is using a lot of oil; I can’t see any smoke- is it burning it?	450/452
A Well how much is a lot, if it’s more than 500ml (half a litre per 500 miles 1L per 1000 miles) then yes, the engine may be on a downward spiral. It’s Likely that the oil control rings are gummed in place by carbon, allowing excess oil to enter the combustion chamber and be burnt in the normal combustion process. The temperature inside the turbocharger unit is high and the oil is almost evaporated by the time it gets to the exhaust and the catalytic converter, so you rarely see smoke on a hot engine. Monitor accurately the oil consumption and the miles covered and contact to discuss options. It will consume more oil until one of two things will happen and there is no cheap fix :-(
1. An exhaust valve will burn away as the engine will be running extra hot when low on oil and the oil burning much hotter than just fuel - this usually causes the engine to go onto two cylinders, and it will have no power and will sound strange
2. If maintenance has been sporadic the next thing to go will be a spark plug, the electrode will overheat if the oil is to low or oil will cover the plug and foul it - either way it will misfire. See note why is the correct oil and fuel and plugs so important.

Q My Roadster interior door handle does not work, why?	452
A There is a cable and on the end is a barrel pin that locates in the door mechanism, this works its way out, usually there is nothing broken it can be refitted and secured to reduce the chance of it happening again.

Q My Steering is stiff, someone said it might be my power steering?	450/452
A Well its unlikely to be that on a 42 as most don’t have power steering, it more likely to be the universal joint in the steering column, there are two, one inside the car and one outside the car but under the under tray, it is exposed to all the water and rubbish thrown up from the roads, there are two options replace the steering column or to remove it and clean it and re lubricate it and replace it.
2 Check the power steering fuse, then the control box connection, check for corrosion and good fit, contact cleaner may help. If still not working properly then it needs to go on a star diagnostics machine and have someone experienced have a look. It could be the control box, the electric motor or steering column or steering rack
3 Roadster yes it could be your electric power steering, they can work intermittently causing the steering to be easy or difficult as the power steering goes on and off again, clean and check the electrical terminals and check the wiring if it continues it may require a new power steering and rack

Q My paddle steering wheel is not working properly, it does not change gear on one side properly or it is intermittent	450/451/452
A Its probably the steering wheel angle sensor failed, they cannot be bought separately, only as a whole steering wheel. It need to go on a diagnostic machine to verify, if this is the case a new steering wheel is the answer. The car looks to the steering wheel angle sensor to see how much steering input you have when deciding how to brake safely in an emergency. Safety note; the abs and ESP may not work properly in an emergency if these are faulty.

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Q When I accelerate I get a whistling noise that goes up and down with the revs?	450/452
A It sounds like the turbo has a damaged inner part, the impellor blades can spin at 2000 times a SECOND and any damage to these special blades will make a whistling noise

Q When I change gear the is a little 'Ptchew' noise I can hear, is something wrong?	450/452
A Well If the boost level is increased or a free flowing air filter fitted you will hear this noise, it the sound of the boost in the turbo being released as the throttle is closed, this is normal

Q Can I just replace the valve that’s burnt out?	450/452
A No it will burn out very quickly, it would be like putting a plaster on a broken leg, the problem will happen again (as quickly as 3 weeks, we have seen very unsatisfactory repairs), the only satisfactory option is to replace or get a professionally rebuilt engine. The condition of the bores and the pistons and rings may determine if the engine will need a rebore and new pistons.

Safety notes
Nb this is intended as a guide and as such not a replacement for a trained technician working on any vehicle but a guide to understanding the workings and problems encountered with the Smart in all its guises
Never work under an unsupported vehicle, always use the correct tools and never attempt jobs beyond your training/capabilities. Always disconnect the battery before working around airbags and seat belt housing as both contain explosive devices, watch out for hot parts or fluids.

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