What To Check If Your Mercedes Turns on But Won’t Start

Luxury, exceptional engineering, comfort, safety, and performance… are the five fundamental qualities of every vehicle that rolls off Mercedes’ assembly line. But despite all the effort the company made to make its vehicles flawless, they can occasionally run into troubles… like struggling to start. This post discusses what you can do if your Mercedes fails to start despite continuous cranking.

First, Verify the Basics

Step #1- Check the battery

If your Mercedes turns on but won’t start, the first component that needs to be checked is the battery. The reason is simple… it powers the components responsible for breathing life into the engine.

Here’s what to check…

• Measure the output voltage of the battery.
• If the readings are below 12 volts, there may be an issue with the charging system… or, the battery may have lost its charge holding capacity.
• It is also important to check the battery terminals.

Step #2- Confirm there is enough fuel in the tank

Once you’re done inspecting the battery and are assured that everything is fine with it, the next thing you should do is check the fuel tank―even if the fuel gauge reads full. There have been instances where people got fooled by erroneous readings displayed by defective fuel gauges.

• Check the fuel tank…
• Consider filling it up if there is not adequate amount of fuel left in the tank.
• Consider replacing the fuel sensor if it is found to be defective.

Inspect The Fuel System

Component #1- Fuel pump

You won’t be able to start your Mercedes if its fuel pump is struggling to deliver the requisite amount of fuel into the engine. There are a few things you can do to assess the condition of your Mercedes’ fuel pump.

One way to do so is to…

• Turn the key to ‘ON’ position and listen for a soft humming noise (from the fuel tank).
• If you hear nothing, or a loud noise instead of a quiet murmur, the fuel pump may be defective.

Component #2- Fuel filter

A clogged fuel filter can restrict fuel supply to the engine... make it a tough job for the engine to start. A defective filter can cause more harm than just preventing the engine from starting… It can contribute to numerous performance-related issues, including stalling, misfiring, rough idling, etc.

• The fuel filter in your Mercedes can become clogged for many reasons… like the accumulation of dirt, debris, and rust from the fuel tank.
• Consider replacing your Mercedes’ fuel filter as recommended by the manufacturer.

Component #3- Fuel injectors

Fuel injectors are responsible for spraying a specific amount of fuel into the combustion chamber at a precise interval. It is because of these small cylindrical components that internal combustion engines now operate with such high efficiency. Defective injectors won’t be able to supply the fuel the engine needs to start its operation.

Signs your Mercedes’ fuel injectors are defective;

• Performance-related issues like misfire, stalling, hesitation, sluggish acceleration, etc.
• Illuminated Malfunction Indicator Lamp
• Fuel burning odor inside the cabin
• Dense black exhaust smoke

Check The Ignition System

#1- Ignition coil/ spark plug

The ignition coil helps spark plugs generate electric sparks. If there is something off with the coil, the spark will be weak or non-existent… which is something that can prevent the engine from starting. Issues with the spark plugs can also prevent the engine from firing up.

To be sure if this is what’s preventing your Mercedes from starting;

• Check the spark plugs for signs of wear and carbon fouling.
• Use a multimeter to test resistance of ignition coil.

#2- Crankshaft position sensor

Based on real-time data received from the crankshaft position sensor, the Engine Control Unit determines the timing of spark plug firing. If there is something off with this sensor, spark plugs won’t be able to fire properly… which can prevent the engine from starting.

It’s quite easy to determine if your Mercedes’ crankshaft position sensor is faulty.

• Get a diagnostic tool and use it to assess the functioning of the crankshaft sensor.
• Consider replacing the sensor, if it is sending erroneous data to the ECU.

In Conclusion

So, these are among the leading reasons why your Mercedes might turn over but won’t start. A blown fuse, faulty relay, issues with the key fob and immobilizer, anti-theft system errors, freezing weather, recent repairs/ modifications, and defective ECU can also prevent your Mercedes from starting.

Motronix, a well-known local auto repair center at Dania, FL since 1988, has been providing outstanding service and repair for Audi, BMW & Mercedes as well as specialized service for Hybrid vehicles.