my Honda Civic 9th Generation (2012-2015) has a check engine light and code P0171

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before starting any work.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Vacuum gauge, hose clamps, screwdriver.
• Check all vacuum hoses connected to the intake manifold for cracks or disconnections.
• Replace any damaged hoses or clamps as necessary.
• Test the intake manifold gasket for leaks using a vacuum gauge; replace if found defective.

3. Clean the Mass Air Flow (MAF) Sensor

• Tools Required: MAF cleaner or electrical cleaner, soft cloth.
• Disconnect the MAF sensor connector and remove the sensor from the air intake.
• Spray the MAF cleaner onto the sensor elements carefully without touching them.
• Allow it to dry completely before reinstalling the MAF sensor.

4. Inspect the Fuel System

• Tools Required: Fuel pressure gauge, wrench set.
• Connect the fuel pressure gauge to the fuel rail.
• Start the engine and check the fuel pressure; it should meet the manufacturer's specification (usually between 40-50 psi).
• If pressure is low, inspect the fuel pump and fuel filter for clogs or failures, and replace as needed.

5. Test and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, wrench.
• Check the operation of the upstream oxygen sensor using an OBD-II scanner for voltage readings.
• If readings are outside the normal range (0.1 to 0.9 volts), remove and replace the sensor.