What is an ESL in Mercedes Benz C 300?

This blog will explain the purpose of ESL in Mercedes Benz C 300 and answer the following questions: what are the symptoms of faulty ESL in Mercedes Benz C 300? How to fix the ESL in Mercedes C 300? How to tell if your Mercedes C 300 has an ESL or not?

What is an ESL in Mercedes Benz C 300?

An ESL in a Mercedes Benz C 300 is a device that prevents the steering wheel from turning when the key is not inserted in the electronic ignition switch. ESL is also known as an electronic steering lock or simply a steering lock. It is found in all Mercedes Benz cars with a third generation of the drive authorization system.

The use of ESL is not limited to the third generation of the drive authorization system or DAS. It is used in models that have a manual transmission. As the manual transmission lacks a P or parking gear, the ESL acts as an additional security measure.

In Mercedes C300, ESL is present in the third generation of the C class W204. It is directly connected to the electronic ignition switch. When the key is inserted in the ESL, drive authorization starts and a start enable signal is issued to the EZS.

The EZS or electronic ignition switch can then be turned into the ignition position 1 and 2. The process is very fast and the ESL unlocks the steering as soon as the key is inserted into the ignition lock.

As the ESL or electronic steering lock is one of the components in the drive authorization system, it is not possible to swap or replace the part with a used ESL. The other components in the drive authorization systems are ECU or engine control unit, transmission control unit (only in automatic C300), and ESP control unit.

What are the symptoms of faulty ESL in Mercedes Benz C 300?

The symptoms of a faulty ESL in a Mercedes Benz C 300 are as follows:

• The vehicle cannot be started and no lights turn on in the instrument cluster.
• The key can be inserted but does not turn in the electronic ignition lock
• The steering wheel of the car does not turn, even when the vehicle is unlocked.
• The vehicle can only be locked or unlocked but the engine cannot be started.

The symptoms of a faulty ESL in a Mercedes Benz C 300 are very similar to when the main battery of the vehicle is completely discharged. Therefore it is a common mistake to assume that the battery of the C 300 is dead when the ignition cannot be turned ON.

One of the most effective ways to identify the two problems is by turning on the radio and interior lights. The radio and the interior light in the C 300 are connected directly to the power supply from the battery.

Therefore, if the radio or interior lights are working then the battery is okay and the fault lies in the drive authorization system of the vehicle. If the main battery is completely dead then the vehicle cannot be unlocked and a mechanical key must be used to unlock the driver’s door.

How to fix the faulty ESL in a Mercedes Benz C 300?

There are two methods to fix the faulty ESL in a Mercedes Benz C 300. Both the methods are described below:

The authorized workshop method

If the ESL in the Mercedes Benz C 300 is faulty then the vehicle must be towed to an authorized dealership. The Xentry diagnosis tool is connected to the vehicle, only the authorized diagnosis tool is capable of running a drive authorization system test.

The test procedure involves inserting the key into the electronic ignition lock and turning it in all positions. It is recommended to run the test with both the original keys of the vehicle for an accurate result.

When the test is over, the Xentry system will show whether the ESL is faulty or not. In some models, the ESL must be replaced along with the electronic ignition lock. Replacing only the ESL will not rectify the fault.

After replacing both the ESL and the electronic ignition lock, a workshop key is used to transfer the drive authorization data to the new control units. This workshop key is shipped with the spare parts and it is not given to the customer.

The vehicle can be returned to the customer after performing the control unit start-up and tech-in of the original key. Overall, the cost of repairs in this method is high but the security of the vehicle is not compromised.

The unauthorized workshop method

It is possible to fix the ESL fault in the Mercedes Benz C 300 without visiting the authorized dealership. In this method, the old ESL is removed from the vehicle and the electrical circuit is extracted from the housing.

The faulty part in the ESL is a locking actuator that locks the steering column when engaged. The electrical circuit that is responsible for the drive authorization and sending the start to enable signal is okay.

This circuit is then installed in a plastic housing and connected back to the C 300. In this method, there is no need to transfer the drive authorization data as the control unit is not replaced. The cost of the repair is also very cheap as only the faulty part is isolated from the ESL and the control unit is reused.

The drawback is there is no longer any means to lock the steering wheel of the vehicle. It is a big security risk as the steering can be turned without the key. There is no fault code present in the control unit as there is no inbuilt position sensor in the ESL to detect if the actuator is engaged or not engaged.

The method is not recommended. The transmission can be put into a neutral position by disconnecting the detent lever and the parking brake is also mechanical so the vehicle can simply be towed away.

How to tell if your Mercedes C 300 has an ESL or not?

The fault in the ESL is a very common problem observed in the third generation of the Mercedes Benz C Class. If the car is repaired in an unauthorized workshop then one of the clear signs is checking the steering wheel.

If the steering wheel turns without inserting the key then the ESL is removed and only the control unit is present. The ESL also makes a noise when the key is inserted in the ignition lock, if the noise does not come then the ESL is not present in the C 300.

Conclusion

This blog explained the use of ESL in Mercedes Benz C 300 and the methods to fix when the ESL is not working. The ESL is considered a theft-relevant part, Hence it must be destroyed if it is replaced. Always consult an authorized workshop when faults are related to the drive authorization system.