Parts: W140 key’s evolution

The key for the W 140 is one of the most common questions in ownership. Why do some users say their keys still work, and why are some refused by dealers? Why can some users order keys in North America, but not in Europe? Are there differences between the different keys for the W 140? How compatible are they? Here we present the most common key models for the W 140 and explain their differences.

With the predecessor, keys were never a problem. A skilled roadside locksmith could duplicate the key of every Mercedes from the first to the late 80s in 5 minutes, but with the 140, it was a bit harder. Generally speaking, the development of the 140 went through a period of rapid development of car anti-theft systems, which was caused by the environment in the world at that time. In Europe, a large number of car thefts occurred after the opening of the West German border, and these cars were sold to the new Russia that wanted S-classes. In Asia, China opened up to private cars, and a large number of S-classes were stolen from the United States and Japan. In the United States, Mercedes thefts are commonplace, and the new S-class is just more valuable. In summary, engineers must always stay ahead of thieves, which leads to frequent updates of anti-theft systems, including keys.

Here we will mainly introduce the evolution of keys, not the key blade, but the key that starts the car in the popular sense. This must include the key fob, which is the remote control. The complete anti-theft system is a larger topic, which we will discuss later. Of course, since the change of keys is mainly due to the update of the anti-theft system, we will also mention some evolution of the anti-theft system in passing. Fahrberechtigungssysteme (driving authorization systems), or FBS for short. FBS is divided into several generations according to the different stages of system development. In this topic, keys are also classified in this way.

FBS 1

New features

• Driving authorization system as standard for the first time

Characteristics

• Start lock
• Shift lock for automatic transmission
• External locking cylinder override
• Steering lock with predetermined breaking point
• Starter encapsulated

Functional description

As soon as the 140 was launched, it was equipped with the FBS 1 key. There are 4 keys in total, two master keys that can activate all the functions of the car. A valet key can only drive the car but not open the storage box. There is no remote control, its appearance is similar to the Mercedes keys of the past, with the same key embryo on models as long as 107 and 126.

The range of delivery of such a key depends on the situation. Before MY1995, if the car was not equipped with the SA code 880 (closing system with infrared remote control) or SA code 030 (FBS 2), the car was delivered with such a key. If you only have such keys, then they can easily be copied by a locksmith even if Mercedes dealers no longer offer them.

FBS 1a

New features

• Driving authorization system as standard for the first time
• Access authorization via infrared remote control
• Infrared receiver on driver’s door and rear lid

Characteristics

• Start lock
• Shift lock for automatic transmission
• External locking cylinder override
• Steering lock with predetermined breaking point
• Starter encapsulated
• Feedback via display next to IR sensor
• Identified by code 880 (locking system with infrared remote control)

Functional description

Unlocking/locking the vehicle
The key transmits the transmitter signal as an infrared light beam to the receiver. The receiver picks up the light beam, filters out extraneous light, amplifies the transmitter signal and passes it on to the infrared remote control (IRC) control unit. The control unit decodes the transmitter signal and, if the code is correct, activates the central locking, arms or disarms the electronic locking system (SA) and controls the comfort control (SA). At the same time, the control unit adjusts to the next code and locks the previous one. If the key is operated outside of the reception range, the code in the key changes, but not in the control unit. If the key is used again within the reception range, the code of the key does not match the code calculated by the control unit. The control unit can only extrapolate to a limited extent. Therefore, the key must be resynchronized if a certain number of times the key is operated outside of the reception range are exceeded.

First version of FBS 1a, dark grey. It made Huf became the first automotive supplier worldwide to develop an infrared key. It was first installed on the 129 in 1989. The infrared remote control was produced by Siemens.

EPC part number: no longer exist
Actual part number: A1297600006 / A1297600106

The delivery range includes vehicles with SA code 880 before MY1994 or August 1993. Each vehicle also comes with three mechanical keys (one each) in addition to two infrared keys.

They are placed in a box. Such key was discontinued long ago when MY1994 started or after August 1993. Part numbers are also deleted in EPC. This one is unique and will not be confused with other key fobs.

The second version of FBS 1a, in black and smaller. The earlier version has no bracket on battery cover.

EPC part number: no longer exist
Actual part number: A1407600306

The modified version comes during MY1995 has a bracket on battery cover.

EPC part number: A1407600406
Actual part number: A1407600306 / A1407600706

The delivery set is the same as before, but no longer comes with a storage box. The scope of delivery depends on the market. In Europe it starts with MY1994 and ends with A238344. In some regions such as the US and Australia it lasts until the end of MY1995. This key replaces the previous larger grey remote control in the Mercedes aftermarket and is the only one that dealers can offer if a new key is needed for a car from MY1994 or before August 1993. EPC calls such key A1407600406, which is different to the two part numbers that appear on the actual key fob. At this moment they are also no longer available.

To make the remote control works on FBS 1a need a matching IFZ control unit (N54). If you want to use the remote control of another car on a different car, you also need the IFZ control unit of another car. Therefore, it is feasible to transplant the anti-theft system between different cars of the same period.

FBS 2

New features

• Infrared receiver and display on the interior mirror
• Spare key in credit card format with mechanical key and remote control function

Characteristics

• Activation/deactivation via infrared remote control
• Intervention in the engine control (dialogue via CAN or PWM)
• Diesel without engine control unit with electronic shut-off valve on the injection pump (dialogue via CAN)

Functional description Unlocking/locking the vehicle
The key transmits the transmitter signal as an infrared light beam to the receiver. The receiver picks up the light beam, filters out extraneous light, amplifies the transmitter signal and passes it on to the infrared remote control (IRC) control unit via a control line. The control unit decodes the transmitter signal and, if the code is correct, activates the central locking, arms or disarms the electronic locking system (SA) and controls the convenience control (SA). At the same time, the control unit adjusts to the next code and blocks the previous one. The feedback light is activated on the driver’s door handle and on the interior mirror. If the key is operated outside of the reception range, the code in the key changes, but not in the control unit. If the key is used again in the reception range, the code of the key does not match the one calculated by the control unit. The control unit can only extrapolate to a limited extent. Therefore, the key must be resynchronized if a certain number of times the key is operated outside of the reception range.

EPC part number: A1407601206
Actual part number: A1407600706

The exterior is same as the previous model, but the functionality is very different. The delivery range in German version started from A238345 or December 1994. It ended at the end of MY1996. Since January 1, 1995, insurance companies only provide theft insurance for cars equipped with this system. For some certain markets that provide Europe version (such as Austrilia), and North America and Japan version, it was only installed on MY1996.

Starting from FBS 2, to start the car, must have an IFZ control unit (N54) match the ECU (N3/10), because the ECU must also be unlocked by the remote control. Once the original key is lost, a new key matching the ECU must be obtained, thus the IFZ control unit between different cars are not interchangeable.

FBS 2a

New features

• Separation of access and driving authorization
• Driving authorization via key with transponder
• Remote trunk lid unlocking (HDF) (SA)
• Feedback via indicators
  

Characteristics

• Infrared remote control via receiver on the interior mirror
• Feedback (red/green) via the interior mirror
• Self-arming by removing the key from the ignition lock
• Intervention in the engine control, dialogue via CAN
• Lock cylinder on all types only on the driver’s door and at the rear
• The spare key (in credit card format) is a full-fledged vehicle key. The infrared function is integrated in the card and the transponder required for starting is integrated in the key bit

Functional description Unlocking/locking the vehicle
The key transmits the transmitter signal as an infrared light beam to the receiver. The receiver picks up the light beam, filters out extraneous light, amplifies the transmitter signal and passes it on to the infrared remote control (IRC) control unit via a control line. The control unit decodes the transmitter signal and, if the code is correct, activates the central locking, arms or disarms the electronic locking system (SA) and controls the convenience control (SA). At the same time, the control unit adjusts to the next code and blocks the previous one. If the key is operated outside of the reception range, the code in the key changes, but not in the control unit. If the key is used again in the reception range, the code of the key does not match the one calculated by the control unit. The control unit can only extrapolate to a limited extent. Therefore, if a certain number of operations outside of the reception range are exceeded, the key must be resynchronized. If the vehicle is locked and the infrared control unit receives a valid infrared code sent by the key via the interior mirror receiver, the infrared remote control (IFZ) control unit controls the central locking, the feedback lights in the interior mirror (approx. 3 s, red: lock, green: unlock) and the indicators (lock: 3 x, unlock: 1 x). If the vehicle is locked and the ignition is switched on (IR control unit detects a valid transponder signal), the vehicle is unlocked and the green feedback light is activated. If the supply voltage is < 9 V, no IR signal is detected and no function is triggered. After a power failure, the state in which the control unit was before the power failure is restored.

Functional description Start engine
The driving authorization (release of the engine control) is independent of the infrared remote control and the battery status of the key. It is achieved by exchanging a valid alternating code between the transponder in the key and the infrared remote control (IFZ) control unit via the coil on the steering lock. After the ignition is “on”, the coil is supplied with energy by the magnetic field created by the transponder. The driving authorization code is then transmitted to the infrared remote control (IFZ) control unit via the transponder. If the validity has been recognized, the engine control is released via communication between the infrared remote control (IFZ) control unit and the engine control unit. When a speed of >20 km/h is reached, the data block read from the transponder is written with new content.

EPC part number: A1407601406 / A1407602006
Actual part number: A1407601406

In USA/Japan vehicles, the central locking, the EDW (SA) and the comfort locking (SA) can be controlled via the locking cylinders (lock nut switches) in the driver’s door and on the rear lid in addition to the infrared remote control. The feedback lights and the indicators are not controlled.

FBS X

New features

• The FBS X driving authorization system is based on the FBS 2a (immobilizer via transponder). It is supplemented by scope 1a (infrared remote control with external receiver).

Characteristics

• Only for US vehicles (code 491/494)
• Operation via IR transmitter key and mechanical key
• Self-arming by removing key from ignition lock
• Driving authorization via infrared key with transponder
• 3 IR receivers:
  •Type 202/210 driver’s door/rear/interior mirror
  •Type 129/140 driver’s door/passenger door/rear
• Feedback only occurs at the controlled receiver
• Two control units (IFZ 1a and FBS 2a)
• Intervention in the engine control (dialog via CAN)

Functional description Unlock/lock vehicle
Unlock vehicle
If the vehicle is locked and a valid IR code is received, the vehicle is unlocked. The green feedback on the respective IR receiver that is being controlled flashes. If the vehicle is unlocked mechanically via the locking cylinder, the vehicle is also unlocked centrally. However, the green feedback is not activated.
Lock vehicle
If the vehicle is unlocked and a valid IR code is received, the vehicle is locked. The red feedback on the respective IR receiver that is being controlled flashes. If the vehicle is locked mechanically via the locking cylinder, the vehicle is also locked. However, the red feedback is not activated.

Functional description Start engine
The driving authorization (release of the engine control) is independent of the infrared remote control and the battery status of the key. It is achieved by exchanging a valid alternating code between the transponder in the key and the infrared FBS control unit via the coil on the steering lock. After the ignition is “on”, the coil is supplied with energy by the magnetic field created by the transponder. The driving authorization code is then transmitted via the transponder to the infrared FBS control unit. If the validity has been recognized, the engine control is released via communication between the infrared FBS control unit and the engine control unit. When a speed of >20 km/h is reached, the data block read from the transponder is written with new content.

EPC part number: A1407603306
Actual part number: A1407600706

The range of delivery of FBS X only include MY1997 of North America version. It is very easy to be confused with FBS 2a or earlier keys. The FBS X mark located under the battery can be used to identify it. Compared to previous versions and contemporary European versions, the system has an independent infrared system. The N54 does not have to be matched with the N54/1 to rely on infrared to unlock the car. Therefore, when the North American MY1997 vehicle loses the infrared key, the key and N54 from other cars can be transplanted.

FBS 2b

New features

• Access and driving authorization via control unit Radio remote control for central locking (radio
  FBS) (for type 168 SA)
• Selective unlocking (driver’s door and fuel filler flap)
• Automatic locking when driving off (can be switched off)
• Re-locking if neither door nor tailgate has been opened after 40 s
• Key with additional PANIC button only for USA

Characteristics

• Transponder for data transmission
• Radio reception antenna in the interior
• Feedback via indicators
• Intervention in the engine control (dialog via CAN)
• Self-arming by removing the key from the ignition lock

Functional description Unlocking/locking the vehicle
The radio signal is read directly into the FBS radio control unit. The antenna is designed as a throw antenna in the area behind the instrument cluster. If a valid radio signal is received in the FBS radio control unit, a signal is sent to the PSE or the instrument cluster (type 168) and to the EDW (SA). The indicators are activated in parallel (1 x for unlocking, 3 x for locking). Global/selective unlocking By pressing the lock and unlock buttons at the same time (until the LED lights up), the key can be reprogrammed from global unlocking (all doors, rear lid and fuel filler flap) to selective unlocking (only driver’s door and fuel filler flap).

Functional description Start engine
The driving authorization (release of the engine control) is independent of the radio remote control and the battery status of the key. The exchange of a valid alternating code between the transponder in the key and the radio FBS control unit is achieved via the coil on the steering lock. After the ignition is “on”, the coil is supplied with energy by the magnetic field created by the transponder and the driving authorization code is transmitted via the transponder to the radio FBS control unit. If the code is valid, the engine control is released via communication between the radio FBS control unit and the engine control unit. When a speed of >20 km/h is reached, the data block read out of the transponder is written with new content.

EPC part number: A1407603806
Actual part number: not shown

The delivery scope includes MY1998 and the MY1999 for North America. The North American version comes with an additional panic button. This is the only model year that does not use infrared in the system, and the systems are completely non-interchangeable between different vehicles. However, rekeying is easier, as the technology is commonly used in other newer models, and there are many service centers available. It shouldn’t be a technical problem.