New Replace Remote key, Plastic Case
Components and Assembly
Hazard warning, Car keys. Central locking.

In this photo the hazard warning devise is indicating that the facility is operating, and should normally only be used when the vehicle is stationary and presenting or indicating a hazard. the highway code however makes an exception to this rule. Quote. You MUST NOT use hazard warning lights whilst driving unless you are on a motorway or unrestricted dual carriageway and you need to warn drivers behind you of a hazard or obstruction ahead. Only use them for long enough to ensure that your warning has been observed. Law DVLR reg. 27 Unquote.

Central locking manual switch.
As important is the central locking facility below the hazard warning indicator lamp, the hazard warning lights will draw attention to the fact that you are in some sort of trouble, and warn other road users of your vehicles presence, while operating the switch below the lamp will secure/lock all doors, boot and fuel filler flap. If you are a female on your own you are advised to ensure this is operated while awaiting assistance. Dropping the widow slightly to check the credentials of your helpers, AA, Police etc. Only where your vehicle is in a dangerous position or likely to be struck by other vehicles or where there is a risk of fire should you leave the safety of your car. Summon assistance as soon as possible, making would be rescue services aware that you are alone and as far as possible making them aware of the location of your vehicle.

The information below was submitted to a forum by an owner who discovered the following, which is worth knowing if only to cut down on repairs to the locking system which is complex and difficult to work on(see also page 53.)
Central locking switch use.
Hi all, Recently found out that you can prevent costly repairs to the central locking system in a very easy way.
Do this test first and convince yourself :
With the car doors locked (with auto-locking enabled or locked with the remote)(be prepared for your alarm to go off) and you sitting inside the car, pull on the inside door handle lightly. Feel the tension on the system and make a mental note of the pressure required to unlock the door. Now use the electric switch (on the dashboard) to electrically unlock the doors, and feel the tension now required to open the door. Much less!
So you ask what the issue is. Well, inside the door there are two thin Bowden style cables the end of which appear to be susceptible to damage if in continuous use. The continuous use of the manual release cable system will cause the cables to fail.
By using the electric release on the dash you will electrically release the lock system and unload the cable (Backup) release system. So remember - push the button below the hazard warning switch, do not just pull the handle. Replacement of this cable/pulley system will set you back a lot of money!!

What locking system has your car got.
It is worth noting that although this site is specific to the A160/2002 W168 there are a number of features that are common to most 'A' Class (face lift 1/3/2001) models, If you are in doubt about what your car was fitted with when New Visit this link and enter your VIN Number that will give you a list of installed items on your car prior to delivery. For instance some 'A' Class were delivered with out central/remote locking this check will confirm the build specification for your car.
thank you Big-John for the reminder of this link/details.

Now the switch below the tri-angle, this will enable you to lock and unlock all doors plus boot at the push of a button this can be confirmed as the plungers on all doors drops when the doors are locked.
However the auto-locking depends on the programming of the switch

This operation will continue until the unit is reprogrammed which unfortunately can be done without the owner being aware, children playing with switches is not only dangerous but can also re-programme the various facilities on the car without the owner being aware.
If this switch is pressed and held for approx 10secs a single or double bleep will be heard.
If a single bleep is heard the car will continue to lock & unlock the doors as the car moves off and stops, a door then being opened opens all doors. This will happen on every occasion of use.
However if the switch is held pressed for a further 10 sec's you will hear a double bleep this indicates that the system has been switched off and no locking action will take place.
The re-establish the auto locking mode simply press the switch for a further period of 10 seconds or until the single bleep is heard and the auto locking mode has been re-programmed.

Also Note, If you unlock you car using the remote key fob and DO NOT OPEN any of the doors or boot, the locking system on your car will re-lock the car after 40-60 seconds automatically this is a safety feature and not a defect.

When first getting your car particularly if a used vehicle, check that the key blade supplied with the car will operate the door and boot lock, yes it may well operate the ignition BUT if the barrels in the locks have at some point been replaced they may not open the car manually, This recently happened to one owner who found the only key he had provided with the car would not open the door or boot when the automatic function failed, he eventually had to force the door to gain access to the car when he was then able to re-synchonise the remote key fob, although he can now gain access using the fob he cannot enter using the blade of the fob in either door or boot locks

Doors Auto lock

Do remember that there are several sets of curcumstances where the car doors will automatically lock, if for instance working on the boot or door locks ,ensure you have the keys on your person, if they are laying on a car seat for instance the car will auto lock and you will be locked out of the car and this car is difficult to enter with out first breaking a window or quarter light.
Another instance is where you unlock and enter the boot first without opening the drivers door, close the boot and the car will lock complete with your keys in a jacket or laying on boot floor this happened to me 30 miles from home, In my instance I had no answer other than to ask my sone to bring me up the spare key

The problem arose when car automatically locked he having disconnected and earth cable.
Ignition keys/ Remote keys
Look After Your Keys latest quote 9/2/2011 195.00 each

Keys sold with the 'A' Class seem to vary considerably every new model seems to come with something different in respect of keys so ensure you get what your car is sold with.
One of the most important items on the car , without them you are going nowhere! to operate the folding key simply press on the small button and the actual key will appear, to unlock your car press the lower section of the key which does have unlock symbol moulded into the plastic case of the key. As you press the Key the cars indicators will flash once. when you lock the car pressing the appropriate section they will flash three times.

Alternative unlocking sequence for your car. There are two alternatives available for unlocking your 'A' Class using the remote key fob:- Press the UNLOCK and all doors unlock.
Press unlock and only the drivers door unlocks, Press the unlock again and the remaining doors unlock
In both instances all doors lock when the LOCK is pressed on the fob.
This unlocking feature can be changed to suite the owner by:-
Press and hold both sections of the fob LOCK/UNLOCK for 6-10 secs, when you use the fob the alternative to the of original setting will be programmed, this will continue until re-set.

Ignition Lock Damage
They say that prevention is better than Cure, well in the case of changing the ignition lock that is true .
Most of us are guilty of the same habit? Putting all our keys onto one string, far more convenient! until you loose them? Or indeed until the wear the barrel in the ignition lock ,.
But I hear you say I haven't got many on my key ring ! Well do this test flip the MB key ready as fitted in the ignition, now hold the bunch of keys supporting the bunch by the MB key blade only! That's the weight/stress your ignition lock barrel is under all the time the keys are in the ignition, that's without the motion of the car and thus keys! Yes it will eventually wear the barrel causing ignition lock/starting problems.
My bunch which isn't large still weighs 130grams(4.6 ozs ) The MB fob key on its own only weighs 41 grams (1.4ozs) it doesn't want much working out as to why the switch wears out!
Ok so the photograph on the left is a bit exaggerated but it makes the point.
Another point worth noting with the locking mechanism,
Most owners use only the remote locking facility on the car which effectively means the mechanical mechanism of the lock never sees the key . If this is the case with your car make sure you keep the mechanism of the locks lubricated with 3 in 1 oil and that the sprung loaded shutter is working when you enter and remove the key , this will help to ensure that the mechanism is kept free of dirt and water which may prevent you using the lock should you ever need to, do not forget the boot lock as well.
This job is on the service list but from my experience does not get done!

Testing the battery in the fob, press the lock section of the key for approx two seconds and you should see a red light flash if this is the case your Testing the battery in the fob, press the lock section of the key for approx two seconds and you should see a red light flash if this is the case your battery is ok, if not get it replaced as soon as possible.

Key Fob Batteries
Key fob batteries appear to go on forever, but of course in truth they are all right one day and fail the next, so as a wise precaution against getting locked out of your car it pays to replace them at least on every 'A' or 'B' service that way you will be able to rely on them. They are inexpensive and can be purchased from MB parts when having your car serviced or fit them when doing the service yourself. And do not forget your spare key, the last thing you want is a sulphated/leaking battery left in the fob, the small contacts are such that they will be easily damaged probably beyond further use.

Tony a fellow owner of a A150 W169 has sent the following information:-Quote
I purchased six batteries in one go. Rapid Batteries provide an excellent service. I was informed that
my order had been processed and a copy of my bill was attached
On looking through the fob replacements page. I see that your fob like mine for my new 150 (New Model W169 model) and uses the same batteries.
In our case it is the CR 2025 battery. This company sells the CR 2025 at a very low price per battery. Less if 5 or more are purchased at the same time.
Thanks Tony it all helps to keep running I have mailed Rapid batteries to see if they can help

A most helpful Company.

Although the above company were unable to help with the Scorpion alarm battery pack they have been most helpful and do sell as Tony says, batteries suitable for your remote key fobs, computer, and many other electrical items. Use the link above to take a look. click back to return to this site

Within the fob there are two batteries of the type that can be seen, many of us have the self same battery in our PC's as backup for the clock date etc, this type of battery is not a specialist battery to MB and can also be purchased at places like Halfords. However experience has shown that it pays to fit and check them in store, one owner having replaced his batteries still could not open his car. It turned out that one of the pair of batteries purchased was duff. Exchanged he was able to open his car no problem, lesson learned!

Note that the batteries which sit on top of one another and will have the positive terminal up towards the cover, ensure the contacts in the unit are clean, any tarnish can be removed with a 'cotton bud' take extreme care not to bend the contacts.
When handling the New battery do so by holding the outer edges, this will avoid moisture from the skin contacting the working surfaces. Take these precautions and your new batteries will last a long time. Before installing New batteries wipe the batteries surfaces with a damp cloth and dry clean before installing, this removes the thin film of contamination that is caused by the batteries gassing off
It appears as a Grey film on batteries that have been installed for long periods and it will affect the conductivity between the two batteries and the fob contacts.
Place them in as shown in the photo and then replace the cover which will snap closed. If you have surgical tweezers available, i.e., plastic NOT METAL use them for installing your batteries.

When Trevor found he had a defective key fob he put it down to batteries, however they did not cure the key fob problem..
Further investigation and he found that whoever had fittet the previous set of batteries had in fact bent the side contact almost double See A which prevented the contact making with the edge of the top battery, the effect of this was that only the lower battery was powering the fob which of course wouldn't then operate the remote key.

If you do experience this problem take great care when straightening the contact pin, brake it off and you will render the romote portion of the key useless.

I would only undertake a battery change when the key fob had been in a warm conditions for an hour or so , the plastic on this type of unit is brittle when cold.
Bearing in mind the cost of a replacement fob, it is worth checking your fob to ensure the batteries are free of any verdigris (build up of green coloured crystals on the battery surfaces, which will in time damage and erode the component parts, and impair the function of the fob. Replace batteries immediately if found in this condition, try and ensure all traces of contamination is removed before fitting the replacement batteries, they are quite cheap from places like Halfords being obtained for just over a 1.00. If it is necessary to clean off residual/contamination do so with extreme caution or you will destroy the component parts rendering your fob useless.

It easier to put the new batteries into the recess of the fob than to put them in the lid, there are directions on the side of the cover for its removal as well as the position of the batteries, although it is difficult to see. Good job the camera could see it? I have highlighted what information I can see!

The actual directions can be seen on the side of the cover the two arrows are indicating how to remove the lid, I was able to remove it with finger pressure , will conditions are warm It is little wonder electrical components of this nature fail when you see how the dirt and dust had accumulated in the recesses of the fob.

We are now able to safely operate our remote knowing that it will work, but remember to carry out the test above having reassembled your fob.

Re Synchronising Remote Keys with engine immobiliser /Auto lock/Unlock
I would point out that I personally have not had to employ either of the following procedures.
Synchronising transmitter signal for key fob remote control. I am reliably informed that this procedure only applies to keys that have already been pre-programmed to your car. New keys purchased from MB will pre-programmed to your car's ECU in Germany prior to delivery to your MB branch.
However if you have remote key that having been programmed to your car fails to either unlock or lock your car and on which the battery test above is satisfactory, it may well be that it wants re-synchronising with your locking system, Mercedes-Benz direct the following be carried out:-

A. Press the locking (2) or unlocking (3) Twice momentarily.
B. Within 30 seconds turn the key to position 2

Press black button 1 to release sprung loaded folded key blade from fob.

My Central locking will not operate any doors or boot lid.
Test the battery in your Fob , replace as required.
Try your spare key fob before going further.
Manually unlock you boot, Check the vacuum pump and well. this is Located left hand side lower section, front of boot space (Spare wheel area) If water is present in the well or the well is flooded the vacuum pump cannot work. Go to page 41 for details and action.

Why is it sometimes necessary to re-synchronise my ignition key? The following information on this site may help you understand, it also make you aware just how intricate modern vehicles are, at least it appears it is helping to make cars more secure? all you have to do now is make sure your car keys are secure! Remote keys and rolling codes? Worth reading

Dave a fellow owner had a bad experience when his ignition switch and transponder coil complete with keys somehow managed to part company with his car steering column, he managed to get the switch back but was left with the transponder coil hanging on it is wire., With the advise and help from the breakdown service they managed to get the car started, this was accomplished by placing the spare key, which fortunately Dave's wife had with her close to the misplaced transponder coil (ring) whereupon they were able to start the car. Its worth bearing in mind that the ignition key is normally situated in the centre of the transponder coil when presented correctly.
Mercedes-Bens service dept finally replaced the ring back in it is correct location and did this FOC ( free of charge ) Needless to say it should not have come out in the first place, if you have this unfortunate experience take great car to ensure the transponder ring is supported and that no stress is placed on the cable, break this connection and your will definitely not start the car , the message 'START ERROR' will appear on the instrument cluster display panel.
This is the same message you will get if you use an invalid key or if the key requires re-synchronising with the immobiliser. Do not confuse re-synchronising with coding, the initial coding is done when the key is purchased from Mercedes-Benz be it with the car or on production of evidence as to your ownership of the vehicle in question.

I recently received an E-mail from an owner stating that one of his keys wouldn't start the car, after a couple of mails it was determined that the casing of the faulty key was cracked and although had worked Ok wouldn't now start the car the car bringing up the 'Start error' message on the instrument display, Although this has not been confirmed by the owner I confident that the transponder pea has gone missing from the cracked casing which would produce this problem, the pea is very small but is the component coded to your car's immobiliser, if your keys casing splits take great care to ensure the pea dose go missing or you will not be able to start your car without a spare key coded to YOUR car
Remember if you are tempted to purchase a key from E-bay or a breakers yard you will require the complete assembly the 1 key, the 2 lock barrel, the 3 transponder that will match with the transponder pea housed within the key fob and the 4 retention ring without all 4 components the key is next to useless.
Your existing keys will not work with this lock nor can they be re-coded or synchronised to work with the replacement lock.

When Eugene a fellow owner experienced problems with the ignition locking barrel he was given this advise :-
1. Get what they call a "workshop" barrel & key. Cost ex Merc is around 70. The barrel can then be installed as is in which case you need 2 keys, one to open car & the other to start. Or you can get a lock-smith to modify the new barrel to take the existing key. I got a barrel for less than half ex another supplier & will see about the lock-smith
2. Get matched lock & barrel ex Merc for about 200. That means it will take the current keys.

As Rod od the Algarve found many long term intermittiant starting issues can be solved by replacing the ignition switch part no.A1684600304
Rod thank you for the feed back .25/5/2017

The procedure implemented by Mrlapou below should only be attempted as a very last resort. Possible re-set facility!
In normal circumstances the remote key fob is not a serviceable item apart from replacing the batteries and keeping it clean, So when Mrlapou's packed up after six years use and wouldn't respond to new batteries he resigned himself to buying a new unit fearing that it would cost the earth! Having decided a new unit was the answer he decided there was nothing lost in having a 'tinker' with the old unit, like you do! And having cleaned the contacts and replaced the batteries for the 'umpteenth' time found that the defect which was indicated by the LED continuously flashing was still present and no the unit still didn't work. He then noticed the two contacts, Marked 'A' in the photo, and being the inquisitive person he is, and knowing he could not make matters worse shorted the two contacts with a screw driver blade. He then re-inserted the batteries, and guess what? To his utter surprise and no doubt the disappointment of MB the unit worked correctly and at the time of going to print is still working. Now whether this is a long term repair has yet to be seen but it certainly works, so if your unit fails in the same circumstances it might just be worth a try, after all what have you got to loose, apart from a possible 100 on a new unit.
The Symptoms of Defect,
Remote Unit fails to transmit a signal to lock or unlock the car, when examined closer the built in LED is continuously flashing.
Remember do all the other checks batteries, clean terminals first. Also try the above key re-synchronising procedure itemised above,

Spare/Replacement Key Fobs
Please note This section of my site has changed due to me having received conflicting information. I have therefore updated it with the latest information available.
Replacement remote key fobs can only be ordered through MB and are very expensive in excess of 100.00 + vat has been mentioned. Fobs are available on e-bay where it is claimed they are suitable for the 'A' Class the only major problem is they do not say which 'A' Class or where it is located!!!! Equally the key being sold may well have been rejected during production by the manufacturer in the first place, by 'Siemans' the Manufacturers.

who have confirmed that they do sell the rejected keys, so that the components, switches, resistors etc can be salvaged, as can be seen there are many components in one key fob.

However one component not shown is a devise about the size of a grain of wheat, which is sealed within the plastic casing of the remote key and is coded to the transponder which surrounds the ignition key location slot, when these two components are in close contact the immobiliser will be disabled and you will be able to start your car, However if you use another remote from another Mercedes vehicle, even fitted with your own key blade the car will not start, as the two transponder components will not be compatible.
Even if you buy the keys and the transponder ring as was on sale on E-bay recently and fit them to your vehicle it is doubtful it will start, this is because there are other components that make up the complete security unit all of which must be compatible I.e. coded the same. I will not pin point their location as it is part of the security system of your car.

1 = LED, 2 battery contacts, 3 switches.

This photograph kindly provided by a fellow owner shows the location of the transponder pea, his key was defective because the crystal had broken living in the far eat he was able to get the key repaired for 10 approx so he got off light. however getting the casing apart is not an easy job and doing so usually writes the key off.

Either way the keys cannot be re-programmed to work with your car's ECU/transponder/immobiliser this has also been confirmed by two Major Mercedes-Benz Main Dealers. THIS INCLUDES THE NEW 'SMART' KEY USED ON THE NEW A' CLASS
If you purchase New keys from Mercedes they will want chassis numbers and well as other proof of ownership before ordering you another key.
Please be aware that the above key fob was CUT open to display the components, The case's cannot be salvaged for re-housing the components of your own fob.
If on the other hand your key is defective because of a damaged blade then you will be able to get a new blade and have it cut using your spare key or photograph as the pattern.(see below)

If the need arises due to damage of distortion to the blade, then it can be removed by removing the small pin using a fine drift, your newly cut blade can be fitted into your existing key. The key Blade can be provided and cut by e-mail for approx 11.00

There are two types of blade but the locksmith in question will determine the type from you photograph. No synchronising is required where your original remote key fob is used.

Having removed the pin,3 pull the old blade from the fob, replace with your key newly cut blade, ensure the blade is round the right way, oval cut-out towards the pin.

In this instance because only the blade has been replaced no other action is required other than to make sure your new blade fits the ignition and door

For suspect or defective starter switch see page 70.

Unlocking Doors and boot manually
Where doors have been locked using the remote they should be unlocked using the remote, if they are forced or even opened with the key blade the car alarm will sound, the alarm can be switch off using the remote buttons providing the remote fob batteries are sound, failing which the car RED or black alarm dongle key would have to be used.

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