why does my BMW 3 Series E90/E91 struggle to start in cold weather?

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is on a level surface and the engine is off and cool.
• Disconnect the negative battery terminal to prevent accidental short circuits.

2. Battery Inspection and Replacement

1. Inspect the Battery:
   • Remove the battery terminals and clean any corrosion with a wire brush.
   • Check for any swelling or damage to the battery casing.
2. Test the Battery:
   • Use a multimeter to measure the battery voltage.
   • If voltage is below 12.4 volts, recharge the battery or replace it if it fails to hold a charge.
3. Replace the Battery (if necessary):
   • Remove the battery from the vehicle using a socket set.
   • Install the new battery, ensuring terminals are tightened securely.
   • Reconnect the negative battery terminal.

3. Starter Motor Inspection

1. Check Starter Connections:
   • Inspect wiring to the starter for signs of wear or damage.
   • Tighten any loose connections.
2. Test Starter:
   • Disconnect the starter and test it outside the vehicle by applying direct battery voltage to it.
   • Replace the starter if it does not engage properly.

4. Fuel System Check

1. Inspect Fuel Pump:
   • Listen for the fuel pump operation when turning the key to the "ON" position.
   • If no sound is heard, test the fuel pump relay and replace if faulty.
2. Check Fuel Pressure:
   • Connect a fuel pressure gauge to the fuel rail and verify that it meets manufacturer specifications.

5. Oil Viscosity Check

1. Inspect Engine Oil:
   • Check the oil level and condition; if it is too thick for cold temperatures, consider changing to a lower viscosity oil recommended for cold weather.