why does my Volkswagen Golf MK5 (2004-2008) have a check engine light with code P0171

Solution

1. Preparation

• Gather tools and parts needed for repair.
• Disconnect the battery to ensure safety while working on electronic components.

2. Inspect and Clean MAF Sensor

• Remove the air intake duct to access the MAF sensor.
• Use MAF sensor cleaner to clean the sensor.
• Allow it to dry completely before reinstallation.

3. Check for Vacuum Leaks

• Visually inspect all vacuum hoses for cracks or disconnections.
• Use smoke testing or a propane torch (without igniting) to locate any leaks.
• Replace any damaged hoses as necessary.

4. Fuel System Inspection

• Connect a fuel pressure gauge to the fuel rail.
• Turn the ignition on (without starting the engine) to check pressure; compare it to manufacturer specifications (typically 50-60 psi).
• If pressure is low, check the fuel pump and fuel filter for clogs or failures.

5. Inspect Fuel Injectors

• Remove the fuel rail and inspect injectors for clogs or leaks.
• Use an ultrasonic cleaner if necessary to clean the injectors.
• Replace any faulty injectors.

6. Oxygen Sensor Check

• Use a multimeter to test the voltage output of the upstream oxygen sensor.
• If readings are outside the normal range (0.1 to 0.9 volts), replace the sensor.