BMW won't start in cold weather
BMW may not start in cold weather. This can affect all BMW including 1, 3, 5, 7, X1, X3, X5 series. Typical symptoms include the engine turning over slowly, then starting. You may be able to start the BMW by either cranking the engine several times or waiting until it gets warmer which is not the ideal solution.
This is a list of items that can prevent a BMW from starting in cold weather.
The first thing you need to check is the battery. This problem can be due to a battery that's near the end of its life. Battery performance decreases as the temperature decreases, therefore it may be harder to start the car if it is cold outside.
BMW may not start in cold weather for several other reasons. Especially if the engine is turning over without a problem, the battery is charged but the engine refuses to start.
Follow this guide on how to change a BMW battery.
Bad Fuel Pump Relay
The fuel pump relay may stick when the outside temperature drops drastically. To verify this remove the fuel pump relay. Take it inside and warm it to room temperature. Do not use methods that would melt the relay. Reinstall it while it is still cold outside and try to start the engine.
If the engine starts, when the relay is warmed replace the relay.
Weak fuel pump
A bad fuel pump can also cause this problem. If you have a fuel pressure gauge, you can easily check the fuel pressure in the morning.
Another test you can perform is to cycle the ignition on three or four times, without cranking the engine. This should build up the required pressure to start the car.
Engine temperature sensor / PCM Coolant Sensor
The engine coolant temperature sensor may also be malfunctioning making it harder for your BMW to start in the morning. Read the fault codes from the Engine Control Unit (DME). If you have fault codes related to the engine temperature sensor, replace it.
Old spark plugs
Spark plugs can there were never replaced can prevent your BMW from starting in cold weather.
If you are using high octane fuel, try using regular fuel to determine if the fuel is the issue. High octane fuel requires a higher temperature to ignite.
Try regular gas.
The variable intake valve control system may be the reason why your BMW won't start. VANOS adjusts the valves during engine warm up for best fuel/air mixture ratio. VANOS is designed to adjust valves at high RPM but can also impact the cold weather performance.