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Mercedes-Benz of Stevens Creek

Mercedes-Benz C 300 Not Starting - How To Troubleshoot and Fix

Issue: Dead Battery

A common reason for a non-start is a defective or dead battery. Find the battery first. It is located on the front engine bay or upper front cowling. Then, start looking for clues. Do your door locks work? Are your dome lights or headlights turning on? Turning the ignition key and being welcomed by a series of flashing lights without hearing the engine turn over is the strongest indicator that your battery is dead.

If you are experiencing a dead battery, here are some steps you can take to fix it:

  1. Pull up a running car next to the car with the dead battery. You want just enough separation so the jumper cables can reach both hoods. Place both cars in park.
  2. Find the battery on the dead car and locate the positive (red) and negative (black) cables.
  3. Retrieve a pair of jumper cables. Any hardware store or auto shop should have them on hand.
  4. Use your red (positive) jumper cable and clamp it to the positive terminal of the dead battery. The positive terminal should be indicated with "POS" or "+". Establish a good connection against the battery post by clamping your jumper’s copper head flush against the metal posts.
  5. Attach the other red cable to the working car's positive terminal and attach one of the black clips to the other car's negative terminal.
  6. Rest or clamp your last black clip on an unpainted metal surface so that it does not cause a spark.
  7. Turn your vehicle's ignition switch and try to start it.

Once your car starts, a best practice is to drive for roughly 10 minutes to help recharge your battery. If you turn off your vehicle and restart it later unsuccessfully, it may mean your battery is no longer capable of holding a charge. Look to have it replaced as soon as possible.


Issue: Faulty Starter

A faulty starter is a very common reason for a Mercedes-Benz C 300 not starting. It is responsible for cranking your engine to life when turning the ignition switch. Repeated clicking, grinding, or loud noises when cranking the ignition is a telltale sign your starter is faulty.

If you are experiencing a faulty starter, be sure to check for battery/connection issues and a faulty trigger circuit. If it is time to replace and install a new starter, the process is relatively straightforward. Removing your starter and solenoid requires raising your vehicle using jack stands, disconnecting your battery's negative cable, and removing all retaining bolts and wires from the starter/solenoid before installing your new starter. When it is time to replace, make sure you get an OEM Mercedes-Benz starter.

If you continue to have issues troubleshooting, seeking replacement parts or performing the repair, a certified Mercedes-Benz technician will be able to help.


Issue: Clogged Fuel Filter

Mercedes-Benz C 300 fuel tanks are magnets for contaminants such as dust and dirt. This debris can clog the fuel system and gas will not be able to pass through to your pump. A fuel filter is used to trap these particles. Signs of a defective fuel filter include engine hesitation upon acceleration, engine failure to start, activated check engine light, or a faint gas smell caused by a fuel leak.

As a best practice, fuel filters should be replaced every 150,000 miles.

In the event you want to troubleshoot the issue yourself, here are the following steps.

  1. With the engine off, disable the fuel pump by removing the fuel pump fuse from the fuse box.
  2. Reduce fuel line pressure by starting the engine and setting the vehicle to 'Park ' with the parking brake on.
  3. Turn off the engine.
  4. Disconnect the fuel lines from the filter and place the new filter in the same spot as the old filter.
  5. Replace the fuel pump's fuse in the fuse box.
  6. Start your Mercedes-Benz C 300 engine and check for filter leaks.

When it comes time to replace your fuel filter, make sure you get a new OEM Mercedes-Benz fuel filter.

Issue: Faulty Ignition Switch

Ignition switches are an integral part of your vehicle, allowing power to be distributed to your Mercedes-Benz C 300's electrical system from the battery. A faulty ignition switch can result in a dead engine, loss of lighting, and key removal issues. If you are in the need of purchasing the items required to replace your ignition switch make sure you get OEM Mercedes-Benz ignition parts.

All in all, there are a variety of reasons why a Mercedes-Benz C 300 won't start. If you are uncomfortable performing any of the above diagnosis or troubleshooting tasks, we recommend taking your vehicle into your local certified technician/dealership.