Mercedes won’t start or turn over? Are you experiencing Mercedes-Benz no start problems? Key won’t turn at all? Engine turning 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 in few cases troubleshooting by a professional is required, there are several test that you can perform yourself to avoid a repair bill. In order for your Mercedes-Benz to start there are several conditions that need to be met and also needs:
1. Start enable by Drive Authorization System
2. It requires electrical power to crank the engine.
3. Requires fuel
4. Requires spark
Top 5 Mercedes-Benz no start problems
1. Engine Click, No Start
2. Engine Dies Right After It Starts
3. Car turns over, but it won’t start
4. The car makes a clicking noise but won’t start. Hint: Starter Problem or Low Battery
5. Key will not turn the ignition
Step 1: Verify that battery is fully charged
This may seem obvious, but an old battery is the root of many headaches and can cause all sorts of malfunctions on Mercedes-Benz cars. How old is the battery on your Mercedes Benz Diagnostic Scanner?
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 the price of the battery, head over to Amazon and check out these batteries that fit Mercedes-Benz. They cost much less than the battery you purchase at the dealership. You can check price and read reviews for multiple Mercedes-Benz AGM Group 94 Batteries that will fit your Mercedes-Benz.
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, Fuel Pump. There could be more circuits that impact the starting depending on the model. You can easily check all the fuses if you are not sure, to make sure none of them are not burned out. Keep in mind that fuses are there to protect systems when they malfunction. Make sure to replace the fuse with the same ampere rating fuse. There is a chance the fuse could blow gain, shortly after that.
To test the fuses, you can use any digital multimeter to easily and quickly check the fuses without removing them. In the video tutorial below we used Mastech AC/DC Digital Multimeter.
Step 3: Check Gear Selector / Brake Light Switch
The brake light switch is a common culprit and frequently fail on Mercedes-Benz cars. The Drive Authorization System will not allow starting the car if the brake light switch is not working properly. In some cases, you will notice this problem because you can’t get the car out of park. Gear shift stuck is one of the most common problems with Mercedes-Benz cars. Unfortunately, looking to see if the brake lights turns on while you press the brake pad, is not a good test to tell if the brake light switch is working properly. This is because the brake light switch has two or more micro-switches inside and only one of them controls the rear brake lights.
Another way to verify if the gear selector module is working properly is to look at the instrument cluster. Now, as you move the shifter from Park to Reverse to Neutral, do you see the gear indicator also 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 USD, just do a search for Mercedes-Benz Brake Light Switches. In the video below you will can see how easy it is to replace the brake light switch on a Mercedes-Benz E-Class. The procedures are very similar for other Mercedes-Benz models such as CLS, S, C, ML, R-Class.
Step 4: Fuel Problems, Mercedes Won’t Start
Is the engine turning over? Let’s eliminate the possibility of a fuel system problems. Troubleshooting fuel related problems is not very difficult and you can check the fuel pressure yourself. Checking the fuel pressure is very simple.
For this test, you will need a fuel pressure gauge. What you need is a fuel pressure gauge with Schrader valve adapter. A great and affordable gauge that we have used in the past is this Actron Fuel Pressure Gauge which works on Mercedes-Benz cars. Turn the engine off and connect this gauge to the Schrader valve test port shown in the picture below. Start the car and you should be able to get around 60 psi. When the engine is running and when you turn off the engine the pressure should stay steady. Always perform this test on a cold engine.
Next, make sure that the fuel injector connections are secure and not loose.
test fuel pressure at schrader valveCheck the fuel pump and the fuel pump relay. In some Mercedes-Benz models you will be able to hear the fuel pump when you listen carefully near the fuel tank. While one of your friends turn the key to position II, all dash lights on but 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, listen through the fuel fill 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. Make sure that it is old and clogged. They can be easily replaced in most cases and don’t cost very much.
Step 5: Check engine fault codes
If your Mercedes-Benz starts and dies then another thing that you can do is retrieve the fault codes.
An iCarsoft MB II or Launch Creader VII+ will be all that you need to retrieve fault codes.
These two scanners will pull the fault codes from the ECU but also from TCU, SRS, ESP, ETS, BAS and several more control units.
Step 6: Starter Motor Problems – Mercedes won’t turn over
If the starter is defective you will not be able to get the engine to turn. First check the starter fuse. Often times, when the starter is defective or seizes up it will blow out the fuse that protect the starter circuit. Another thing that you can try is to hit the starter with a rubber hammer a couple of times.
Depending 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.
Step 7: Ignition system, Spark Plugs/Coils – Mercedes starts then dies
If your car cranks but it does not start there are two things that you should check first. One is that there is fuel and second that there is spark. Checking for spark is very easy if you have an In-Line Spark Test Tool.
As you will see from the link, those tools are very inexpensive and a great tool to check for spark. 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.
Step 8: Check Crankshaft position sensor – Crank No Start
If the crankshaft position sensor fails you may experience crank and no start symptoms. In this video below you will see 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.
In this Video you car see a Mercedes-Benz that cranks but won’t start do to failed crankshaft position sensor.
Step 9: Driver Authorization System / Key won’t turn in igntion
The car may not start if you have a newer car with a SmartKey due to Driver Authorization System (DAS) failure. The newer keys have a transponder integrated in them. The key fob remote serves two purposes. First it disables the anti-theft system when you unlock the car. Second, Drive Authorization System verifies the key to make sure it is the right key to start the car.
If your key does not turn the ignition, there are two things that are the most likely scenarios: The battery is fully or partially discharged. This doesn’t allow the electronic ignition system (EIS) to function at all. Make sure to verify that you don’t have a defective battery problem. Second, the Driver Authorization related problems. 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 electrical ignition module (EIS) can only be performed by the dealership and typically costs over $1000-$2500. Keep in mind that the key can often be the problem and not the DAS or EIS. So if you have a spare key, try that first before you replace the EIS. Keys do go bad 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 to not start. If you check all of the things 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 Autel DS708 Professional Scanner, powerful scanner that works on most makes and models.
Once you hook up a professional OBD II scanner to the OBD-II port of your car, you will be able to scan multiple systems on your car to find out 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
Fault codes related to driver authorization or immobilizer
In rare cases, you may also have a locked up engine due to lack or oil or hydro lock. Low compression or blown head gasket can also cause a Mercedes-Benz car not to start but are not very common problems.
We hope this guide helped you start your Mercedes-Benz. As you perform these test be careful to avoid injuries to yourself and damages to yourself. If you don’t feel comfortable with some of these test, it’s better to take your car to an auto repair shop.