Mercedes-Benz Will Not Start: Step by Step Troubleshooting Guide

Last updated: October 29, 2026

Can’t start or turn over your Mercedes-Benz? Are you experiencing Mercedes-Benz no-start problems? Won’t the key turn at all? The engine turns over, but the car will not start. Maybe it finally starts, runs for a few seconds, and then dies. These are common Mercedes-Benz starting problems.

This comprehensive step-by-step guide is written to help you with Mercedes-Benz no-start issues. While troubleshooting by a professional is required in a few cases, there are several tests you can perform yourself to avoid a repair bill. For your Mercedes-Benz to start, several conditions need to be met and also needs:

1. The Drive Authorization System has to authorize the key before anything else happens
2. It requires electrical power to crank the engine.
3. Requires fuel
4. Requires spark

Start here: match your symptom

What the car does when you turn the key narrows the cause faster than working through every step in order. Find your symptom, then jump to that step.

Top 5 Mercedes-Benz no-start problems

• Engine Click, No Start

• Engine Dies Right After It Starts

• The car turns over, but it won’t start

• The vehicle makes a clicking noise but won’t start. Hint: Starter Problem or Low Battery

• The key will not turn the ignition

Step 1: Verify that the battery is fully charged

This may seem obvious, but an old battery is often the root of many headaches and can cause a range of malfunctions in Mercedes-Benz cars. How old is the battery on your Mercedes-Benz?

While some MB owners have pushed over 10 years on an original battery, the battery should be considered for replacement around 6 or 7 years. If you have an old battery, replace it before you move to the next troubleshooting step. If you want to save on battery prices, head over to Amazon and check out the batteries that fit Mercedes-Benz. They cost much less than the battery you purchase at the dealership. You can check prices and read reviews for multiple Mercedes-Benz AGM Group 94 Batteries that will fit your Mercedes-Benz.

You know you have a relatively new battery. You go to start your Mercedes-Benz, and you either hear it turn over once or hear several clicks, as in this video.

This Mercedes-Benz is not starting because its battery is low. In this case, you need to trickle charge your battery using any of these 12-volt battery trickle chargers. If you need help, read this article on How to charge a Mercedes-Benz correctly.

Step 2: Check fuses and relays

Mercedes won’t start, and it’s not the battery.

Next, you should check the fuses on your car.

You would want to check fuses for systems such as Starter Circuit, Ignition, EIS, and Fuel Pump. There may be more circuits that affect the start, depending on the model. If you are not sure, you can quickly check all the fuses to make sure none of them are burned out. Keep in mind that fuses are there to protect systems when they malfunction. Make sure to replace the fuse with one of the same ampere rating. There is a chance the fuse could blow again shortly after that.

To test the fuses, you can use a digital multimeter to easily and quickly check them without removing them. We used Mastech AC/DC Digital Multimeter in the video tutorial below.

Read DIY Tutorial: How to check all fuses on a Mercedes-Benz, the easy way.

Step 3: Check Gear Selector / Brake Light Switch

The brake light switch is a common culprit and frequently fails on Mercedes-Benz cars. The Drive Authorization System will not allow the vehicle to start if the brake light switch is not working correctly. Sometimes, you will notice this problem because you can’t get the car out of park. A stuck gear shift is one of the most common problems with Mercedes-Benz cars. Unfortunately, checking to see if the brake lights turn on when you press the brake pedal is not a good test to determine if the brake light switch is working correctly. This is because the brake light switch has two or more micro-switches inside, and only one controls the rear brake lights.

Another way to verify if the gear selector module works properly is to examine the instrument cluster. As you move the shifter from Park to Reverse to Neutral, do you see the gear indicator change on the instrument cluster? If you don’t see the letters on the cluster change from P to R to N, it is a good sign that the gear selector module is defective. You can buy a new brake light switch on Amazon for less than $15 and search for Mercedes-Benz Brake Light Switches. In the video below, you will see how easy it is to replace the brake light switch on a Mercedes-Benz E-Class. The procedures are very similar for Mercedes-Benz models such as CLS, S, C, ML, and R-Class.

Read DIY Article: How to replace the brake light switch on any Mercedes-Benz. If you replaced the brake light switch and your car won’t start, move on to Step 4.

Step 4: Fuel Problems, Mercedes Won’t Start

Is the engine turning over? Let’s eliminate the possibility of fuel system problems. Troubleshooting fuel-related issues is not difficult, and you can check the fuel pressure yourself. Checking the fuel pressure is a simple process.

For this test, you will need a fuel pressure gauge. What you need is a fuel pressure gauge with a Schrader valve adapter. An excellent and affordable gauge we have used is the Actron Fuel Pressure Gauge, which works on Mercedes-Benz cars. Turn the engine off and connect this gauge to the Schrader valve test port, as shown in the picture below. Start the car, and you should be able to get around 60 psi. When the engine is running and you turn it off, the pressure should stay steady. Always perform this test on a cold engine.

Next, ensure the fuel injector connections are secure and not loose.

Check the fuel pump and the fuel pump relay. In some Mercedes-Benz models, you can hear the fuel pump when you listen carefully to the fuel tank. When one of your friends turns the key to position II, all dash lights are on, but the car is not started; listen carefully at these locations. Under or behind the rear seat, listen inside the trunk near the back of the back seat, and listen through the fuel filler with the fuel cap removed. The fuel pump should run for several seconds every time you turn the key to position II.

Also check the fuel filter and make sure it is not old or clogged. They can be easily replaced in most cases and are relatively inexpensive.

Step 5: Check engine fault codes

If your Mercedes-Benz starts and then dies, you can also retrieve the fault codes.

The YOUCANIC full system scanner will be all you need to retrieve fault codes. This scanner will pull the fault codes from the ECU and TCU, SRS, ESP, ETS, BAS, and several more control units.

If you need help using an OBD II scanner to retrieve the fault codes, read this article: How to check the fault codes on a Mercedes-Benz.

The YOUCANIC scanner reads every one of those modules, shows you which ones are not responding, and runs bidirectional tests so you can command the starter or the fuel pump directly.

Compared to Xentry

For diagnosing a no start the coverage is effectively the same. Xentry’s unique capability is online VIN coding, which you need when fitting a brand new EIS, not when finding out why the car will not crank. If the repair turns out to be a cloned or repaired EIS, that coding step disappears too.

Step 6: Starter Motor Problems, Mercedes Will Not Turn Over

If the starter is defective, you cannot get the engine to turn. First, check the starter fuse. When the starter is defective or seizes up, it will often blow out the fuse that protects the starter circuit. Another thing that you can try is to hit the starter with a rubber hammer a couple of times.

Depending on what kind of starter problems you have, the starter may work a few more times. Even if the starter begins to work again, consider replacing it, as it is nearing the end of its life.

If you conclude that the starter is the problem, read this article on How to Replace a Starter on a Mercedes-Benz.

Step 7: Ignition System, Spark Plugs and Coils, Mercedes Starts Then Dies

If your car cranks but does not start, there are two things that you should check first. One is that there is fuel, and the second is that there is a spark. If you have an In-Line Spark Test Tool, checking for spark is very easy.

As you will see from the link, those tools are inexpensive and great for checking for sparks. You remove the spark plug boot from one of the spark plugs and install this tool in line. Crank the car and observe the spark plug test tool.

Read DIY Guide: How to replace the spark plugs on a Mercedes-Benz

Step 8: Check the Crankshaft Position Sensor, Crank No Start

If the crankshaft position sensor fails, you may experience crank and no start symptoms. The video below shows a Mercedes-Benz that refuses to start due to a failed crankshaft position sensor.

When the crankshaft position sensor fails, you may notice the following symptoms:

• Check engine light is on.
• Intermittent starting
• Misfiring
• Hesitation
• Engine vibrations
• Engine stall

In this video, you can see a Mercedes-Benz that cranks but won’t start due to the failed crankshaft position sensor.

Don’t panic, though. Replacing the crankshaft position sensor is easy, and the sensor is very inexpensive. Read this detailed article on replacing the crankshaft position sensor on most Mercedes-Benz V6 and V8 engines.

Step 9: Driver Authorization System / Key won’t turn in the ignition

The car may not start if you have a newer car with a SmartKey due to Drive Authorization System (DAS) failure. The newer keys have a transponder integrated into them. The key fob remote serves two purposes. First, it disables the anti-theft system when you unlock the car. Second, the Drive Authorization System verifies the key to ensure it is the right one to start the vehicle.

If your key does not turn the ignition, two things are the most likely scenarios: The battery is wholly or partially discharged. This doesn’t allow the electronic ignition system (EIS) to function. Make sure to verify that you don’t have a defective battery problem. Second, a fault in the Drive Authorization System itself. When you insert the key into the ignition, the key is verified and authorized to start the car.

Once the key is authorized, the steering column is unlocked, and the Engine Control Unit is allowed to start the engine. Replacing the electronic ignition module (EIS) at the dealership typically costs over $1000-$2500, because they fit a new module and program it to the car. That is not the only option. The original module can often be repaired, or its data cloned onto a replacement unit, which costs far less and keeps your existing keys working. Module Medics offers a mail in Mercedes EIS ignition clone service, and also handles EZS repair, key programming including FBS3 systems, ISM shifter modules and ECU repair. Remember that the key is often the problem, not the DAS or EIS. So if you have a spare key, try that first before you replace the EIS. Keys do go wrong more often than EIS modules do.

Step 10: Other Possible Problems, Mercedes-Benz Will Not Start

The list can go on and on as to what can cause a Mercedes-Benz not to start. If you check everything above, you have done most of the work. For this last step, you will need a professional diagnostic scanner. Our top recommendation, in this case, is the YOUCANIC Full System Scanner, a powerful scanner that works on most makes and models.

Once you hook up a professional OBD II scanner to your car’s OBD-II port, you can scan multiple systems on your vehicle to determine what is causing the problem.

Here are a few other items that may prevent your Mercedes-Benz from starting. In most cases, you will get a fault code related to one of the following:

• ECM / PCM computer failure
• Camshaft position sensor
• Shifter selector module or SAM module
• Fault codes related to drive authorization or the immobilizer
• Electrical problems

In rare cases, you may also have a locked-up engine due to a lack of oil or hydro lock. Low compression or blown head gasket can also cause a Mercedes-Benz car not to start, but these are not very common problems.

We hope this guide helped you start your Mercedes-Benz. As you perform these tests, be careful to avoid injuries and damage to yourself. If you are uncomfortable with some of these tests, taking your car to an auto repair shop is better.

Applicable Models

This guide applies to the A-Class, B-Class, C-Class, E-Class, S-Class, CLA, CLS, CLK, CL, SLK, SL, R-Class, GLA, M-Class, GL-Class and G-Class.

Questions from Mercedes-Benz Owners

My Mercedes starts, runs for a few miles, then dies and will not restart until it cools down. What causes that?

A car that stalls when hot and restarts after cooling down most often has a failing crankshaft position sensor or a weak fuel pump or fuel pump relay. Both fail when warm. Read the engine codes right after it stalls, while the fault is still current, and check fuel pressure if the codes do not point to the crank sensor.

It cranks but will not start, yet it starts fine with a jump. I already fitted a new battery. Why?

If a jump fixes it, the starter is not getting enough voltage on its own. Check that the new battery is the correct size and fully charged, then clean and tighten both battery cables and the engine ground strap. A corroded positive cable or bad ground drops voltage under cranking load even with a new battery. On newer models, the new battery may also need to be registered with a scanner.

No crank at all, but the lights and radio work. Where do I start?

If everything powers up but the starter does nothing, check that the shifter is fully in Park, then try the spare key. A key the EIS will not accept, a steering lock that has not released, a failed starter relay or the starter itself are the usual causes. A scan of the EIS and engine module tells you whether the car is refusing to start on purpose or the starter is not responding, and our key will not turn guide covers the EIS side.

We sell the UCAN-II Pro. The function comparisons above come from each manufacturer’s own documentation so you can check them yourself.