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My Key Won’t Turn Ignition Mercedes-Benz Problem

Interior vibrations Mercedes BenzYou insert the key in the ignition of your Mercedes-Benz, but nothing happens. You can’t turn the key. You can’t start the car. The main reaon why this happens is a dead battery, but it can also be several other problems which we have described below. As you insert the Smart Key remote into the Electronic Ignition Switch(EIS) control module (N73), power is supplied to the key by the induction coil ring located in the EIS. Data is then exchanged with the infrared transmitter to validate the Drive Authorization. This article goes over the main reasons why the key won’t turn in the ignition and possible solution.

Mercedes EIS / EZS Immobiliser Key Module Problems

  • Unable To Turn The Key
  • Unable To Start The Car
  • Can Turn The Key  but the car will not start
  • Ignition Key Faults
Drive Authorization System (DAS) is the Mercedes Immobilizer system which checks drive authorization every time you insert the key into the ignition and try to start the car. DAS was introduced back in 1996 and has had several security improvements. The main DAS versions DAS are DAS 2, 2A, X, 3.

List of common problems and possible solutions

  • Locked Steering Wheel

New drivers always experience this at least once, so we thought we would include it in this list. If the key does not turn in the ignition, try moving the steering wheel as you try to turn the key. The steering wheel will feel completely solid if you try to move it in one direction and may move slightly in the opposite direction. Push the steering wheel in the direction that allows a little movement and then insert the key and try to turn the key again. You can put pressure on the steering wheel and also try shaking the steering wheel. As you do this insert the key into the ignition and try to turn the key. DO NOT TRY TO FORCE THE KEY IN THE IGNITION. The steering column lock is a security feature which all car manufacturers incorporate in the cars.

  • Discharged Battery  Undervoltage

It is possible that the battery in the car is defective, as it does not provide the necessary voltage for the ECU and  the N73 Electronic Ignition/Starter Switch (EIS)  to function properly. If the battery is dead or has low voltage / under voltage, the CAN communication between EIS and N72 may not function properly.  The EIS in the Mercedes-Benz has a coil that induces a magnetic field on the Smartkey wich causes the key to respond to the car with a specific rolling code. Using a $10 dollar multimeter like this one, you can check that you have a good battery before you proceed further. The car battery should indicate at least 12.8 volts without the car running. When the engine is running it should be over around 14.4 volts. If you need a replacement battery for

your Mercedes-Benz the most cost effective option would be to order one on Amazon. Most Mercedes-Benz cars use Battery Group 94R and a great choice would be the ACDelco 94AGM Battery which meets the OEM specifications. Click here to read reviews and check the price on Amazon. 

mercedes benz battery group 49amazon check price


  • Key Tumbler Defective

If you have a metal blade key instead of the Smart Key Remote, it is possible that the key tumbler could be defective. While most Mercedes-Benz cars have the SmartKey some models such as the ML Class, SLK Class, Crossfire used a metal blade key up to 2005. Some models suffer from the defective key tumbler. We have seen cars with as little as 20,000 miles where the tumbler go bad. Make sure the steering wheel is not in a locked position as mentioned above. Then insert the key into the ignition and gently jiggle the key without putting much pressure on the key as do this. As the lock pins on the tumbler wear out it will get harder and harder to turn the ignition of your car.  Here is a video that will help you understand this problem. The video below shows the same problem on a GM, but the same principle applies to the older Mercedes-Benz that use a metal blade key.

  • Defective Electronic Ignition/Switch System EIS / N73

The EIS module could also be the reason that the key does not turn when inserted in the ignition. Many car owners complain that the car starts fine on a warm or hot day but in cold days the car will not start. This may sound strange, but it is reported frequently. The EIS has processors soldered on the circuit board and in many cases the connections for the processor could be bad or the processor itself is defective. In the video below you can see how the cold temperature causes the ignition switch to not work properly. The ECU could experience the same symptoms as well.

If you have this problem you will have to install a new / virgin EIS. You can not install a used unit because the EIS has to be paired / married to the car using Mercedes-Benz Star Diagnostic Software.
  • Smart Key Remote

They key itself may be the reason why the car doesn’t start. The key may open the doors, but it will not start the car. In some cases, the transponder coil wires may disconnect and need to be resoldered or the processor in the key could be defective. The simplest solution, in this case would be to order a new key from the Mercedes-Benz dealer. Read What you need to order a new key for your Mercedes-Benz.
  • Defective Electronic Control Module (ECU)

Electronic Control Module (ECU) is another reason why the car doesn’t start. You will need to get a new ECU installed to solve this problem. You can not swap with a used ECU and expect it to work as the board is “married” to the car. Another solution would be to get a used ECU and switch the processor from the old circuit board to the used replacement ECU. Watch this video and see how MBCluster user on Youtube successfully cloned a Mercedes-Benz ECU!

Also consider:

  • Cleaning the EIS keyhole with a dry cloth. Do not use liquid to clean the EIS.
  • Checking Fuses
NOTE: Avoid letting the car’s battery discharge while the key being in the ignition. This could damage the key or the EIS.
Are you experiencing the problem where the Smart Key remote does not turn the ignition? Please comment below to let us know how you solved your problem. This will help others who are dealing with the problem.
 

23 comments

  1. I have a 2001 Mercedes cl500 and the key will not turn the ignition at all. The steering wheel will move and the dash will light up but that is all. The key will not lock or unlock the doors or the trunk.

  2. E500 new key from dealer will not turn ignition but works to unlocks the doors and open the trunk. Is replacing the EIS the only solution to resolve this issue?

  3. My car is a w220 cdi s320
    2001 model my kids was playing with the key after that I went to start at that time key is not terning . And I removed and trod several times once it it got turned but didn’t start after that I removed and again tried so many time it could ent start

  4. My 2010 GL450 key turns all the way to the Start position without difficulty. However this does not turn on any systems that normally are supposed to turn on when the key is in the ON position and the car will not start. I replaced the battery in the key fob. It can lock or unlock the car from more 30ft away.

  5. The mechanic changed so many things in my s350 2006 (shocks, transmission etc) and when he finally brought the car back, i drove it and the next day the passenger door jumped. I parked it and the next day the key would not turn at all and the doors will not close and the battery is fine and the lights come onwhen the door is opened. I am in Africa and it is difficult to get an expert. My car has only 56000 miles on it.

  6. I have a S430 (2004), which has exactly the problem described here. The ignition key will not click in the cold weather. If I leave the key in the EIS long enough (5 min to 15 min), the car will eventually start, but it will also drain the battery. So I took the car to MB dealer (Westwood MA). Sure enough, they told me I have to replace the EIS module. And then the sales guys tells me it will cost $2,800.00 !! I kept myself in check from saying WTF !!. This is a complete rip-off.

    Everywhere I read on the internet, the cost of replacing EIS is $700 – $1200. I also read that you can not buy EIS module from Amazon OR Ebay and just replace it. It has to be done by the dealer. Is that true?

    My car has 250,000 miles on it AND I don’t want to spend that kind of money. Any advice?

    • Unfortunately, you can’t install a used EIS from eBay or Amazon. It needs to be virgin. Some Mercedes specialized shops may be able to help you with this.

  7. I have a Mercedes c300 2009 57000 mil now the steering column control module problème no signals no Cruise no horn no windshield wipers no air bags no radio amplifier the alternator makes noise the dealer manager told some cars are bad luck go trade it or it coast $2500 to be fixed I was shocked Are they sell cars on luck or on the quality

  8. My wife pulled my r350 out of garage to warm up while letting the car warm and raise it cut off and everything died, tried turning key again but wouldn’t turn

  9. I have a Mercedes-Benz 2000 amg edition. My key wont turn the sterring wheel is locked the brakes are locked. We checked all the fuses, we unhooked the battery, jumped the battery, reset the key, tried turning the steering wheel with the key. Nothing seems to work. Any idea what the problem could be? The lights and beeping noise still happens when my key is inserved just won’t turn

  10. What does it mean when my Mercedes key FOB flashes countinuosly in the ignition and will not turn.What does the flashing light mean?

  11. I have 2007 C230 sport and the fob works on everything except starting the car.When I stick it in the ignition the red light flashes continuously and wont turn.Does anyone know why the red light on the fob is flashing?

  12. I have a 1959 220s and the key ,all of a sudden, will not turn in the tumbler. What can I do?

  13. I am very much puzzled with the S series (2001 S430) MB. Aside from water leak from sunroof, water finding its way into SAM underneath back passenger sit, or in the well where you have the modules for speakers, CD changer an what not, the FOB will not work and then work. At first I thought it needed new battery (despite the presence of infra red light at the tip of the FOB) and charging the 12 V battery did not make the FOB turn or start the engine. I tested every relay and fuses on all three SAMsand they all were working. Then I pulled out the EIS module and tinkered around it finding no problem. I put it back the EIS together and by luck I was able to crank start the engine. The following day, battery was drained and I had it recharged> As i connected the negative cable, alarm goes on. Again no amount of depressing panic button would stop it. And from that time on, cant turn on the FOB to start the engine.

  14. The key does not turn or start the car. We checked the battery and the key battery.

  15. My 99 c230 the main key won’t work but the valet did now the valet starts the car but then it immediately turns off I towed it to a shop and they said the key wouldn’t connect to their computer and the code is saying it’s the met? But they aren’t sure that’s the problem

  16. I have the dead battery as i left the key in the ignition for two days, how can i jump start.I tried to jump start but still the key would not turn.

  17. My 2005 S500 has been stored in an unopened steel storage container for 2 and a half years, when I reconnected the battery it still seemed to have a good charge but the electronic key would neither turn nor activate on any function. I have recharged the battery and put new battery in the remote, I will test tomorrow and upload the results! Before leaving the car I put dehumidifiers in and around the car, I must say despite being in damp wales the car looked and smelt perfectly dry and and I am sure ready to go. It was a tight fit getting it in and I was only to get blocks under the rear axle.

  18. Got a merc benz C 180…2000 model . The key won’t open doors,won’t turn on the ignition,literally the key won’t do anything . tried changing batteries….It’s still not working

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