Mercedes Makes Clicking Noise but Won’t Start: What to Do?

Mercedes Makes Clicking Noise but Won’t Start: What to Do?

Have you ever turned your key in the ignition, only to hear a clicking sound, but your Mercedes refuses to start?

In this article, we’ll explore the reasons why your Mercedes might be making this clicking noise without starting.

Quick Answer: Why does my Mercedes just click and won’t start?

When a Mercedes just clicks and won’t start, it often points to an electrical issue. The clicking noise is generally caused by a low battery voltage, a defective starter motor or relay, loose starter motor or battery wiring, or a defective alternator.

4 Common causes and their solutions

Here are four common causes and their solutions for a Mercedes making a clicking noise when starting.

Let’s start with the most common cause:

1. Low battery voltage

Low-voltage battery illustration

When the battery is not working properly, your Mercedes won’t start, and that’s when you hear the clicking noise.

How do you know if it’s the battery?

  • Check the lights. A quick and easy test is to turn on your Mercedes’s headlights. If they’re dimmer than usual, or if they don’t turn on at all, your battery is probably dead.
  • Look at the dashboard. When you turn the key, do the dashboard lights flicker or appear dim? This is another sign that your battery might be running low on power.

Note: Your Mercedes usually has two batteries. A main battery (which can cause a clicking noise if low) and an auxiliary battery.

What could be wrong with the battery?

  1. Age. Mercedes batteries don’t last forever. Typically, they have a lifespan of about 3 to 5 years. If yours is older, it might simply be time for a replacement.
  2. Loose connections. Sometimes, the issue is as simple as loose or corroded battery terminals. These are the connections where the battery links to the rest of the car. If they’re loose or dirty, they won’t conduct electricity effectively.
  3. Drainage issues. If you accidentally leave your headlights on or there’s a hidden electrical issue, your battery might drain faster than it should.

How do you fix it?

  • Jump-start your car. If the battery is the problem, jump-starting your car can help. This involves using another car’s battery and some jumper cables. Remember, red to positive (+) and black to negative (-). After the jump-start, let your car run for a while to recharge the battery.
  • Clean the terminals. If the terminals are dirty or corroded, cleaning them might solve the problem. You can use a simple solution of baking soda and water.
  • Get a new battery. If your battery is old or damaged, it might be time for a new one. This is a straightforward fix and something many car owners learn to do themselves. You can find our guide on replacing a Mercedes battery here!

2. Starter motor or starter relay problems

A starter motor on a mechanic's bench

Another possible cause of a Mercedes clicking but not starting is the starter motor or starter relay.

The starter motor is an electric motor that turns your engine over to start the car. The starter relay is an electrical switch that tells the starter motor when to engage.

Diagnosing starter motor or starter relay issues

  • The sound test. When attempting to start, listen carefully. A single loud click may indicate a malfunctioning starter motor, while rapid clicking often points to the relay.
  • Tap the starter motor. A gentle tap on the starter motor with a tool (like a wrench) can sometimes get it moving if it’s stuck.
  • Test the relay. If you’re comfortable with car mechanics, you can try swapping the starter relay with another similar one in your car (like the horn relay) to see if that solves the problem. If your car starts, then the relay is the issue.
  • Check the connections. Like with the battery, start by checking the connections to the starter motor and relay. Loose or corroded connections can prevent them from working properly.

If you find that your starter motor or starter relay is defective, the only (worthwhile) solution is to replace any of them with a new part.

According to RepairSmith, replacing the starter motor on a Mercedes-Benz typically costs between $440 and $551.

3. Loose wiring

Mercedes GLC 350e engine

Your Mercedes is full of wires that carry electrical signals and power to various systems. If these wires are loose, corroded, or damaged, they can interrupt the flow of electricity, preventing your car from starting.

How do you know if it’s loose wiring?

  1. Visual inspection. Open the hood and take a look around. You’re searching for wires that appear frayed, disconnected, or corroded. Pay special attention to the areas around the battery and starter motor.
  2. Check for loose connections. Gently wiggle the wiring connections. If anything feels loose, that could be your problem.

How do you fix it?

  • Clean corroded connections. If you find corrosion, you can clean it off. A mixture of baking soda and water can work wonders here.
  • Tape up minor damage. If a wire’s insulation is slightly damaged but the wire itself is fine, you can use electrical tape to cover the damage. This is a temporary fix, though – you should eventually replace the wire.

4. Alternator issues

Mercedes alternator

Moving on, let’s talk about the alternator. The alternator charges your battery while the car is running, and if it’s not working right, your battery won’t have enough juice to start the car next time.

It can also cause some common Mercedes fault codes, like ‘Stop Vehicle Leave Engine Running.’

So, if you discover that your battery has a low voltage, it may be caused by a defective alternator.

You can test a Mercedes alternator by following these steps:

  1. Start the engine. Turn on the engine. Keep the car in Park (or Neutral if it’s a manual transmission) and apply the parking brake.
  2. Reconnect the multimeter. Like with the battery test, connect the red lead to the battery’s positive terminal and the black lead to the negative terminal.
  3. Check the voltage with the engine running. With the engine on, your multimeter should now show a higher voltage. Typically, this should be between 13.7 to 14.7 volts.
  4. Load test. Turn on your car’s headlights, air conditioning, and radio. The voltage should remain stable (within the 13.7 to 14.7 volts range). If it drops significantly, your alternator does not supply enough power and is defective.

If you find that the alternator is defective, you should have it replaced.

If you continue driving with a defective alternator, you will see the ‘Stop Vehicle Leave Engine Running’ message frequently, as well as other error messages such as ‘PRE-SAFE Functions limited.’


We hope this guide has helped you find the cause of your Mercedes’s starting problems.

Remember, while some of these issues can be diagnosed and fixed at home, others might require the expertise of a professional mechanic.

Don’t hesitate to seek help when needed, especially with complex components like the alternator or starter motor.

Let us know in the comments below if you have any more questions!

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