Why Your BMW Won’t Start: 6 Common Causes (& Solutions!)

Why Your BMW Won’t Start: 6 Common Causes (& Solutions!)

If you’re here, your BMW probably refuses to start. Trust me, I’ve been there, coffee in hand, running late for a meeting, and all I got was a clicking sound.

It can be downright frustrating!

Sometimes, it’s a pesky battery issue. Other times, it could be something more serious.

Either way, understanding what’s going on can make all the difference.

That’s why I’ve put together this guide. We’ll dive into the common reasons your BMW is not starting and, more importantly, how to get it up and running again.

Note: If you have a BMW 3 Series, we’ve written an article specific to this model not starting here.

6 Reasons why a BMW won’t start (and their fixes)

If your BMW doesn’t start, here is a summary of solutions you can try before taking it to a mechanic:

  1. Check your battery health. Try to jump-start the car or recharge the battery.
  2. Try starting your car with the spare key. Your key or the push start-stop button may be malfunctioning.
  3. Ensure you don’t have a clogged fuel filter, faulty fuel pump, or defective fuel injectors.
  4. Check for any blown fuses or faulty relays.
  5. Diagnose the mechanical systems, including spark plugs, ignition coils, or the starter motor.
  6. In rare cases, your BMW might not start due to air pockets in the fuel or extremely cold weather.

Now, let’s dive into the details!

1. Battery-related issues

The battery in your BMW acts as the electrical energy reservoir, ensuring your engine starts and all other electrical components run.

But like every reservoir, sometimes levels can run low, or there can be leaks.

Cause: Low battery voltage

Low voltage battery illustration

The main signs of a bad battery on your BMW are the following:

  • No or fewer lights lighting up on the dashboard
  • Dimming of dashboard lights while cranking
  • No radio turning on
  • No noise coming from the car

A healthy BMW battery should read around 12.6 volts when the car is off. However, with the engine running, this should increase to between 13.7 and 14.7 volts, thanks to the alternator charging it.

If your BMW isn’t hitting these numbers, the battery isn’t holding a charge as it should.

What is the solution?

If you have a car battery tester (you can find multiple on Amazon, like this one), you can connect it to your battery’s positive and negative terminals to test the battery yourself.

Consistently low readings (below 12 volts when the car isn’t running) indicate it’s time to recharge or replace the battery.

If you see corrosion on your battery’s terminal, cleaning it using a mixture of baking soda and water can also help.

Cause: Parasitic draw draining the battery

If your battery dies frequently, especially after being parked overnight or for extended periods, you might be dealing with a parasitic draw.

Some parasitic draw is normal (e.g., for your BMW’s clock or security system).

However, a draw above 50 milliamps after the car’s been off for 20+ minutes indicates an issue.

Common culprits: malfunctioning door switches, boot lights, faulty relays, or after-market equipment like sound systems.

What is the solution?
  1. Parasitic draw test: With your car off, use a multimeter set to DC amperage. Disconnect the negative battery terminal, then connect your multimeter in series (one leads to the battery terminal, the other to the car’s cable). Readings above 50 milliamps after 20 minutes? There’s a problem.
  2. Isolate the culprit: Keep the multimeter connected and pull out fuses one by one. A sharp drop in amperage after pulling a particular fuse will point you to the offending circuit or component.

2. Ignition and key problems

If your BMW won’t start with a good battery, the next step is to check your key and ignition system.

Cause: Faulty key

Modern BMW keys have an electronic chip embedded within them. This chip communicates with the car’s security system to allow it to start.

If the chip is damaged, missing, or malfunctions, it breaks this line of communication.

You’ll know you have this problem if you insert the key, but there’s no response, or the ignition struggles intermittently. Perhaps the car fails to recognize the key altogether.

What is the solution?

Before concluding that this is the issue, try your spare key. Often, it’s just a faulty primary key.

If your BMW starts with the spare key, replace the batteries of your main key and try again.

If that doesn’t work, visit your BMW dealership. They can provide a replacement or reprogram your existing key.

Cause: EWS (Electronic Immobilizer System) malfunction

The EWS system is designed to prevent theft by only allowing the engine to start if it recognizes the coded chip inside the key.

Over time, or due to electrical glitches, the EWS system can lose synchronization with the key.

You might notice your BMW not starting and displaying a key symbol on the dashboard. Or, you find that the car only starts intermittently.

What is the solution?

Sometimes, simply locking and unlocking the car using the physical key (rather than a remote) can resync the EWS system.

In extreme cases, the EWS module may need to be reset or replaced.

Cause: Malfunctioning ignition switch

The ignition switch sends power to different car components, allowing the car to start. A faulty switch may not send these signals correctly.

So, if pushing the start-stop button results in no start or electrical components (like the dashboard lights) don’t activate, a malfunctioning ignition switch may be the cause.

What is the solution?
  1. Inspect: Check for signs of wear or damage on the ignition switch. Look for loose connections or frayed wires.
  2. Clean: Sometimes, simple debris or dirt can interfere with the switch’s operation. A gentle cleaning might restore its function.
  3. Replacement: Persistent problems will require the switch to be replaced. Given the complexity, it’s recommended to consult a mechanic for this.

3. Fuel system issues

Fuel is the lifeblood of any vehicle, and when there’s an issue with its delivery or quality, your BMW simply won’t start.

Cause: Clogged fuel filter

Clogged fuel filter illustration

The fuel filter is responsible for keeping impurities out of the engine.

Over time, dirt, rust, and other contaminants can block this filter, restricting the flow of fuel.

Reduced engine power, the engine stalling during acceleration, or even the vehicle not starting at all can indicate a clogged fuel filter.

What is the solution?

Check the fuel filter on your BMW. If you notice an accumulation of dirt, it’s a sign that it might be clogged.

It’s best to replace your BMW’s fuel filter every 15,000 to 30,000 miles.

Cause: Faulty fuel pump

The fuel pump sends fuel from the tank to the engine.

If it’s malfunctioning, it can’t maintain the required pressure to deliver the fuel, causing the engine to starve.

If you have a faulty fuel pump, your BMW might not start, or it could bog down and stall when you try to accelerate.

What is the solution?
  1. Listen: Turn your key to position 2 (without starting the car) or press the start-stop button once. If you don’t hear the pump’s typical whirring sound from the rear, there’s likely an issue.
  2. Check fuel pressure: Using a fuel pressure gauge, you can determine if the pump is delivering fuel at the correct pressure.
  3. Replacement: If the pump is faulty, replace it. Always choose high-quality parts, as this is a critical component of your BMW.

Cause: Fuel injectors

Fuel injectors spray fuel into the engine in a fine mist for optimal combustion.

When they’re clogged or malfunctioning, this mist is disrupted, leading to inefficient burning.

Rough idling, reduced fuel efficiency, and difficulty starting are all signs of injector issues.

What is the solution?
  1. Clean: Sometimes, using a fuel injector cleaner added to your fuel can resolve minor clogs. This can be a preventative measure as well.
  2. Inspection: Look for signs of leakage or damage on the injectors.
  3. Replacement: Persistent problems might require a fuel injector replacement. A qualified mechanic should handle this task, given its complexity.

4. Electrical issues

Modern vehicles, especially luxury brands like BMW, have loads of electric systems, sensors, and wires.

When these systems fail, they can lead to many issues, including your BMW not starting.

Cause: Fuse and relay issues

A box of car fuses

Fuses and relays act as protective mechanisms for your car’s electrical circuits.

A fuse will ‘blow’ or ‘burn out’ to prevent excessive current flow, which can damage components or even cause fires.

Relays, on the other hand, control high-current circuits with a lower-current signal, essentially acting as switches.

If your BMW won’t start but everything else, like the lights and radio, works, it may be due to a blown fuse or broken relay.

What is the solution?
  1. Inspect: Check your BMW’s fuse box. Look for any fuses that appear burnt or broken.
  2. Replace: Replace any malfunctioning fuses with ones of the same rating. For relays, if you suspect one is faulty, try swapping it with another of the same type. If the issue is resolved, replace the defective relay.

Cause: Electronic Control Module (ECM) malfunctions

The ECM, sometimes referred to as the car’s “brain,” is responsible for overseeing and controlling numerous systems in the vehicle.

A malfunctioning ECM can lead to a range of problems, from minor glitches to a complete no-start condition.

If the car displays multiple error messages, you likely have a problem with the ECM.

What is the solution?
  1. Diagnostics: Use a BMW scanner to read any fault codes related to the ECM. These codes provide insights into potential issues. The best way to diagnose your BMW is either by using Carly, or the Bimmerlink app in combination with an OBDII reader.
  2. Address the issue: Sometimes, simply clearing the fault codes or resetting the ECM might resolve the problem. However, persistent issues might necessitate a more in-depth diagnosis or even ECM replacement.

5. Mechanical problems

Checking under the hood of a BMW

Engines are complex assemblies of moving parts working to convert fuel into motion.

While electrical problems are the usual suspects when a BMW refuses to start, it’s important not to overlook potential mechanical causes.

Cause: Worn-out spark plugs or defective ignition coil

A row of firing spark plugs (illustration)

Spark plugs ignite the fuel-air mixture in the cylinders. Over time, they wear out or get fouled.

The ignition coil provides the necessary voltage for this spark. A malfunction in either component can cause your BMW to fail to fire up.

What is the solution?
  1. Check: Remove the spark plugs and inspect their condition. Testing each spark plug using a spark tester. If any plugs are not firing, you’ll need to replace them.
  2. Replace: Swap old spark plugs for new ones. If they’re still not firing, it’s likely that the ignition coil is defective.

Cause: Defective starter motor

The starter motor is crucial for cranking your engine.

Over time and repeated use, the starter can wear out or get damaged, preventing it from effectively turning the engine over.

When you turn the key or use the push button, and you hear a clicking sound but the engine doesn’t crank or start, it’s a sign of a weak battery or a defective starter motor.

You’re hearing the clicking sound of the starter solenoid engaging, but the starter motor itself isn’t turning.

What is the solution?
  1. Inspection: A quick way to test the starter is to lightly tap it with a tool while someone tries to start the vehicle. If it suddenly works, this could indicate a failing starter.
  2. Replacement: If the starter motor is determined to be the issue, it needs to be replaced. While some experienced DIYers might tackle this job, many prefer to take it to a mechanic due to the complexity of accessing the starter in some BMW models.
A starter motor on a mechanic's bench

Cause: Mechanical issues like a seized piston

Pistons move up and down inside the engine cylinders.

Over time, lack of proper lubrication or overheating can cause a piston to get stuck or “seize” inside its cylinder. When this happens, the engine can’t turn over.

If you hear a loud, unusual noise and the engine abruptly stops, followed by the inability to restart, it might be due to a seized piston.

What is the solution?
  1. Professional inspection: Due to the complex nature of engine internals, it’s best to have a mechanic inspect the engine to confirm the issue.
  2. Avoid force-start attempts: If a piston is suspected to be seized, do not try to forcibly start the engine. This can cause further damage. Depending on the extent of the damage, repairs might range from freeing the piston to complete engine replacement.

6. External factors

Beyond the internal mechanics and electronics of your BMW, there are also external factors that can prevent your car from starting.

Let’s take a look at how you can identify and address these:

Cause: Empty fuel tank leading to air pockets

If your car struggles or fails to start shortly after running out of fuel and then refueling, air pockets might be the issue.

Running a car out of fuel can introduce air into the fuel lines. When you then refuel, these air pockets can prevent the fuel from flowing to the engine smoothly.

What is the solution?
  1. Refuel appropriately: Avoid running your car until it’s almost or completely out of fuel. This helps in preventing the formation of air pockets.
  2. Clearing air pockets: If you suspect air pockets have formed, you might need to prime the fuel system. Try to let the fuel pump run multiple times without cranking the car by pressing the start-stop button without holding your foot on the brake.

Cause: Extreme cold weather

If your BMW struggles to start on a particularly cold morning, the weather might be the culprit. You may also notice sluggish electronics or slower cranking speeds.

Cold weather can affect the efficiency of the battery, thickening the engine oil and causing fuel to vaporize less efficiently.

This combination can make starting a car more challenging in cold conditions.

What is the solution?
  1. Winter-proof your battery: Cold can sap the strength of your battery. Consider using a battery warmer or parking your vehicle in a garage during extremely cold nights.
  2. Switch to winter oil: Thinner oils, designed for winter use, can help ensure smoother starts in cold conditions.

Conclusion

It’s safe to say that BMWs, like any other machine, are not immune to issues.

And when they fail to start, it can be a frustrating experience.

But you can now diagnose and possibly fix many of the common reasons a BMW won’t start.

It’s always helpful to listen to your car. Often, it’ll give you small signs before a more significant issue arises.

If you found this article interesting, you can learn more about the reliability of BMWs here!

Lastly, if your issue persists, let us know in the comments below, and we’ll try to help!

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