My Key Won’t Turn Ignition Mercedes-Benz Problem

• Unable To Turn The Key
• Unable To Start The Car
• I can Turn The Key, but the car will not start
• Ignition Key Faults

Drive Authorization System (DAS) is the Mercedes Immobilizer system that 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 are DAS 2, 2A, X, and 3.

New drivers always experience this at least once, so we thought we would include it. If the key does not turn in the ignition, try moving the steering wheel as you turn the key. If the steering wheel is mechanically loaded against the steering lock, gently move the steering wheel while turning the key. Do not force the key. If the steering lock does not release and the problem persists, further diagnosis of the EIS/steering-lock system may be required. The steering wheel will feel completely solid if you try to move it in one direction, and it may move slightly in the opposite direction. Push the steering wheel in the direction that allows a slight movement, then insert the key and try turning it 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 INTO THE IGNITION. The steering column lock is a security feature that all car manufacturers incorporate into the cars.

The battery in the car may be defective, as it does not provide the necessary voltage for the ECU and the N73 Electronic Ignition/Starter Switch (EIS)  to function correctly. If the battery is dead, has low voltage, or is undercharged, 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, which causes the key to respond to the car with a specific rolling code. Using a 10-dollar multimeter like this, you can check your good battery before proceeding. Measure the battery after the vehicle has been sitting without charging or recently running. A fully charged conventional 12-volt battery will typically measure around 12.6–12.8 V at rest. A significantly lower reading may indicate a discharged or weak battery. With the engine running, verify that the charging system is operating within the vehicle manufacturer’s specified range. If the battery fails testing, replace it with a battery that matches the vehicle manufacturer’s specified capacity, dimensions, terminal configuration, and battery technology. 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. Battery size and specifications vary by Mercedes-Benz model, engine, production year, and equipment. Verify the correct replacement battery by VIN or the original battery specification.

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, on Mercedes-Benz models equipped with a mechanical ignition lock, a worn key or worn lock cylinder can prevent the key from turning. If the key becomes progressively harder to turn, inspect the mechanical lock system before replacing electronic components. We have seen cars with as little as 20,000 miles where the tumbler goes 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 you do this. As the lock pins on the tumbler wear out, it will get harder and harder to turn your car’s ignition. 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 uses a metal blade key.

The EIS module could also explain why the key does not turn when the engine is on. Many car owners complain that their car starts fine on a warm or hot day, but the vehicle will not start on cold days. This may sound strange, but it is reported frequently. Intermittent EIS faults can sometimes present differently depending on temperature or operating conditions. These symptoms alone do not confirm an EIS failure; the EIS, key, power supply, wiring, and steering-lock system should be diagnosed. The EIS has processors soldered on the circuit board, and in many cases, the connections could be bad, or the processor itself is defective. The video below shows how cold temperatures cause the ignition switch to malfunction. The ECU could experience the same symptoms as well. Engine-control-module faults can cause a no-start condition after the ignition is successfully switched on, but an ECU fault should not be assumed when the key itself will not turn. Diagnose the EIS/EZS, key authorization, steering lock, power supply, and communication circuits first.

If diagnosis confirms an internal EIS fault, the EIS may need to be repaired or replaced. Replacement units require vehicle-specific configuration/programming, depending on the system and replacement procedure.

The key itself may be the reason why the car doesn’t start. The key may open the doors but not start the vehicle. In some cases, the transponder coil wires may disconnect and need to be resoldered, or the key’s processor 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.

Electronic Control Module (ECU) is another reason the car doesn’t start. You will need to get a new ECU installed to solve this problem. A used EIS/EZS is generally not a simple plug-and-play replacement. Depending on the vehicle and replacement procedure, the module must be correctly configured and matched to the vehicle’s drive-authorization system using appropriate Mercedes diagnostic equipment.

NOTE: Avoid repeatedly operating the ignition with a severely discharged battery. Low system voltage can interfere with EIS/immobilizer operation and can create misleading diagnostic symptoms.

What Scanner Can I Use to Troubleshoot Mercedes-Benz Ignition Problems?

If you’re experiencing problems with your Mercedes-Benz, a YOUCANIC full system diagnostic scanner can help you troubleshoot the issues. This advanced diagnostic tool can read and interpret the fault codes stored in your car’s computer system, providing detailed information about any problems with the engine, transmission, brakes, or other critical systems.