Modern Tech
Smart Keys and Keyless Go

by Ken Adams
Master Technician
 
Unlocking the car doors on our modern Mercedes cars with a simple push of a button on the car’s Smart Key has become so commonplace that we don’t give it a second thought. Now, more and more of our cars are equipped with the Keyless Go system so that we don’t even have to take the key out of a pocket or purse. Simply walk up to the car, touch the door handle and the doors automatically unlock, sit down, press the brake and touch the start button to start the engine.

Feature photo: When you take the Smart Key and control module apart, the complexity becomes obvious. Note here the coil around the key socket that energizes the key identification circuits, and the elements on the module circuit board that recognize your key and activate the starter.

We don’t give much thought as to how the car knows that we actually have a key in our pocket, or that it’s the specific key that should activate the systems on this particular car.

Of course, the downside to all this convenience is that if we lose that key, we must visit the dealer for a replacement key which is going to cost several hundred dollars. Gone are the days when we could take the spare key to the hardware store and for a couple of bucks have the helpful hardware man grind us a new key.

So how do these smart and keyless systems work, and why are the keys so expensive to replace?
Let’s start with the locking and unlocking mechanisms that are built into both the Smart Keys and Keyless Go fobs.

Smart Keys use electronics to authenticate the key rather than mechanical tumblers. But how does this function work? The two main systems to process this electronic exchange of data are the Electronic Ignition Switch (EIS) and Drive Authorization System (DAS).

When a smart key is inserted into the ignition, power is supplied inductively to the remote control key by a coil in the EIS. (See photo above) similar to a Sonicare toothbrush charging when put into its base. No wires, right? Because the EIS provides power inductively to the key, a remote with completely dead batteries will still start the vehicle. The batteries only operate the locking and unlocking functions as well as the Panic feature. When the key is inserted into the ignition, infrared communication is shared between the key and EIS. If the code that the control unit receives is correct for this car, an unlock signal is sent to the electronics steering lock to unlock the steering wheel. This is the zip sound you hear on some vehicles immediately after inserting  the key.  (On some later models other theft deterrent systems such as gearshift locking have replaced the steering column lock).

But the authentication process is still not complete. The DAS still has the final say whether an engine is allowed to start. After turning the key to position in the EIS, the engine-control module receives power and a secret data exchange occurs between the engine-control module and EIS. If the corresponding messages match, the engine-control module allows the vehicle to start. If that check was unsuccessful, a fault code is stored in the control module to aid a technician in the event of a failure.

If the key is lost or misplaced, its use can be disabled in the control module preventing unauthorized use or theft of your vehicle. If the key is subsequently found, its access can be restored by recoding the control module.

Quite a bit of technology goes into these keys to allow them to control remote functions while maintaining a high level of security. A replacement key can run approximately $280 plus the labor cost associated with programming of the key to your vehicle. To protect security, the owner is required to provide proof of ownership and a matching valid identification before a replacement key can be ordered.

The remote function transmitters and circuits in the key do require electricity, supplied by a battery in the key. A battery test feature is built into these smart keys. If any button is pressed and held for more than three seconds, and the battery is okay, a small red light will flash. If the light doesn’t flash, the battery needs to be replaced. Because the smart key unlocks the doors, if the battery should fail, you have a standard slotted key inside the key fob that will open the driver’s door.

Now let’s take a more detailed look at what is involved for the system to operate and keep your vehicle secure. In the standard Smart Key systems, a central antenna receives the unlock signal when you press that button, even if you’re 20 meters or so from the car, and the control module unlocks one, and then all the doorsflashes the exterior lights, and turns on the interior lights.

The diagrams from the Workshop Information System (WIS) illustrate all the sensors and actuators that are part of the Keyless Go system.

On cars with Keyless Go, as a general rule, each door is fitted with a Keyless Go antenna, and there is an antenna in the rear of the vehicle for trunk operation. Keep in mind the range of these antennas is very short, (1-1.5 meters); the idea here is to prevent unauthorized entry when you step away from the vehicle.

When you approach the vehicle and actuate a door handle, the antenna reads the coding of your key and determines if this is a valid key for this vehicle. The unlock request is sent to the Keyless Go control module; if authenticated, an unlock request is sent to the central locking system module and the doors are unlocked as requested. With another pair of antennas the system is smart enough to know whether you are inside or outside the vehicle.

Once the vehicle is unlocked and you are seated and ready to go, a few more electronic processes are performed. The electronic ignition switch now comes into play as a secondary antitheft deterrent to prevent a thief from hot-wiring the car. The EIS authenticates the key regardless of whether you are using the traditional key in the ignition method or Keyless Go. Only when all authentication codes are processed and deemed correct can the engine be started and the shift selector be moved out of park position.

The side of the case containing the battery is shown. The battery is accessed by removing the emergency door key and prying open the case.

Keyless Go can now be found on a wide range of Mercedes-Benz models. In models with the gearshift in the center console, the start button was located in the gearshift lever. But since the introduction of the gearshift selector on the steering column, the pushbutton switch is now located on the dashboard where the traditional electronic ignition had been located. Some of the high-performance models have their start button prominently mounted in the console.

In most cases, these start buttons are basically the same ignition switch with a removable Keyless Go button inserted in place of a key. The Keyless Go button can be removed to allow the traditional key to be used if desired.

As with any high-tech device, failures can occur. Here are a few suggestions to help your dealership resolve the issue in a timely manner.

1. Is this an issue that occurs with a specific key or all keys? If it is one specific key, mark that key with tape or something to identify it as the failing key.
2. Is the issue related to a specific door unlocking or locking, but the others work okay? (Faulty door handles are the most common failure.)
3. When bringing your vehicle in for Keyless Go failures, always bring all the keys you have. Sometimes the keys fail and dealerships can determine which key is faulty. We also have the ability to disable a lost or misplaced key as well as reinstate a located key.

 
The History of Mercedes-Benz Ignition Keys

For most of recorded history, people have used devices to keep others from accessing their property. Cars started with simple electric connections, then with tumbler switches and keys with grooves and teeth, then derivations of metal keys, and now electronic keys. Keys for valued Mercedes-Benz cars have followed a similar evolution.

Starting in the 1920s and going into the 1950s, keys were metal with side grooves and notched teeth that fit into a lock and actuated tumblers that allowed the key to turn if everything was correct. Picture 1 (from 1950) shows an example of these short keys with relatively few teeth that limited the number of different key/lock combinations possible. There was a certain amount of faith that two cars would not reside in the same community with exactly the same key/lock setup.

In this picture, the larger key was for the ignition and the smaller key for the door, trunk, and fuel filler door. Often, only the driver’s door had an outside key; all other doors were locked and unlocked from inside the car. By the 1950s some higher-end cars also had a steering wheel locking mechanism built into the lock. A thief might access the door, but picking the lock and releasing the steering wheel would require more drastic and damaging maneuvers.

By the 1960s keys were metal with side grooves and more notched teeth. Picture 2 (from 1960) shows an example of these types of keys. The longer key allowed for more teeth to fit into a lock with more tumblers that provided increased key/lock combinations than were possible with the shorter keys. Still, a skilled thief (or locksmith) could pick these locks and security was lost much as it was with the earlier keys. Steering-wheel interlocks were common in Mercedes-Benz vehicles by this time. In this picture the larger key was for the ignition, the smaller rounded key for the doors, and the smaller rectangular key for the trunk, glove box, and optional locking gas cap.



By the 1970s keys were still metal, but had a larger hand grip and were notched on both sides to make it easier to simply insert the key into the lock regardless of how it was being held in one’s hand. The same style of key still had side grooves and teeth but was harder to “pick” because two sets of tumblers were involved on the top and bottom of the lock. Picture 3 (from 1970) shows an example of this type of key. By this time only one key was provided for the ignition, doors, trunk, and glove box. An optional locking gas or diesel cap came with its own key.



Keys were similar in appearance in the 1980s, with side grooves, but the notches were a bit more complex and had tumblers that responded to the wavy notches in the keys. These allowed for more complex key combinations and thus fewer keys that were exactly the same. Picture 4 (from 1980) is an example of this type of key. As with the previous generation, only one key was provided for ignition, doors, trunk, and glove box. By the 1980s most models had a fuel door that was lockable from inside the car and did not require a locking fuel cap with its own key.



The 1990s keys came with small remote-control devices that electrically opened and locked doors and the key flipped out from the case to access the ignition (and other mechanical locks). Picture 5a shows the case with the key opened. The small button on the front corner released it to flip out from the case and to go back into the case. One benefit was that a key carried in pants pockets did not have the sharp edges of the metal digging into one’s skin.



Picture 5b shows the more complex grooves and wavy notches on both sides of the keys and on both the top and bottom of the groove. This complexity made picking a lock very difficult, if not impossible, and allowed for many more key/lock combinations. Only one key was provided for the ignition, doors, trunk, and glove box. The lockable door was standard for fuel access.



In the mid-1990s the first Smart Keys were released. These were electronically coded to communicate with the ignition lock, release the steering wheel lock, and allow the key to start the vehicle. The remote control function emitted an electronic signal to the doors to open or close. They still had a removable metal key to lock the trunk and glove box if a valet were to have the main key to park a vehicle. Picture 6a shows the key with its removable insert.



Picture 6b shows the top of the key with the door-open, trunk-open, and locking buttons, and the Panic button that would sound the alarm if the driver were being harassed and wanted to get attention or scare away a thief or intruder.

With the advent of the Smart Key, all models came with an alarm system to attract attention to forcible entry. Smart Keys also allowed the key not only to lock the doors, but to close windows and sunroof if they were inadvertently left open when exiting the vehicle. If windows remained  down for an extended period of time – and refused to go up fully – the Smart Key could reset the fully-closed setting on the windows so they would completely close. Yes folks, the keys were truly smart!

The first generation of Smart Keys were longer than the one in pictures 6a and 6b and were subsequently shortened because the longer key, with an owner’s other personal keys hanging off the end put a strain on the ignition lock and caused damage. Mercedes-Benz still recommends that the number of keys hanging from the end of a Smart Key should be limited.

By the 2000s, Mercedes-Benz had developed an optional credit-card sized access control device. The driver simply approached the vehicle with the card in his or her pocket or purse and the doors would unlock, and the lights illuminate. The driver merely pushed the start/stop button on the dash to start the car. Hence, Keyless Go.

The biggest problem with this device was that it was thicker than a credit card, and didn’t stand up to being carried in back-pocket wallets, so the company has reverted to a keyfob-like device that contains the Keyless Go circuitry.
Keyless Go continues to be an optional feature on some models, though it is standard on the high-end vehicles, including the S-Class and SLS.