what to do if my BMW 3 Series E90/E91 fails to start in freezing temperatures?

Solution

1. Preparation

• Gather tools and parts needed: multimeter, socket set, OBD-II scanner, jumper cables.
• Ensure the vehicle is in a well-ventilated area and the parking brake is engaged.

2. Battery Inspection and Replacement

• Sub-step 1: Disconnect the negative battery terminal to ensure safety.
• Sub-step 2: Clean any corrosion from the battery terminals using a wire brush.
• Sub-step 3: Test the battery with a multimeter; if voltage is below 12.4 volts, replace it.
• Sub-step 4: Reinstall the new battery and connect the terminals securely.

3. Starter Motor Check

• Sub-step 1: Remove the starter motor from the vehicle by disconnecting the battery again and unbolting it from the mounting.
• Sub-step 2: Test the starter motor using a jumper cable to see if it engages; if it does not, replace the starter motor.
• Sub-step 3: Reinstall the starter motor and reconnect all connections.

4. Fuel System Inspection

• Sub-step 1: If the fuel pump is not activating, check the fuel pump relay and replace if necessary.
• Sub-step 2: If the fuel pump is operational, check the fuel lines for freeze or blockage.
• Sub-step 3: Ensure the fuel filter is clean and replace if it shows signs of clogging.