how to fix P0171 code in Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather tools and parts.
• Park the vehicle on a level surface and engage the parking brake.
• Disconnect the battery to ensure safety while working on electrical components.

2. Inspect for Vacuum Leaks

• Tools Required: Vacuum gauge, smoke machine (optional)
• Visually inspect all hoses connected to the intake manifold for cracks or disconnections.
• Use a vacuum gauge to check for leaks; a low reading indicates a potential leak.
• If available, use a smoke machine to introduce smoke into the intake system to identify leaks.

3. Testing the MAF Sensor

• Tools Required: Multimeter
• Locate the MAF sensor, typically situated between the air filter and throttle body.
• Disconnect the electrical connector and use a multimeter to check the voltage output while the engine is running.
• Compare the readings to the specifications from the service manual; replace the MAF if out of range.

4. Check Fuel Pressure

• Tools Required: Fuel pressure gauge
• Locate the fuel rail and connect the fuel pressure gauge to the test port.
• Turn the ignition key to the "ON" position without starting the engine to check for initial pressure.
• Start the engine and observe the pressure reading; it should meet manufacturer specifications. If low, check the fuel pump and filter.

5. Inspect Fuel Injectors

• Tools Required: Injector cleaning kit
• Remove the fuel injectors from the fuel rail.
• Clean each injector using a cleaning kit or ultrasonic cleaner.
• Test each injector for proper spray pattern using a noid light or similar tool.

6. Oxygen Sensor Check

• Tools Required: OBD-II scanner, oscilloscope (optional)
• Use the OBD-II scanner to monitor live data from the oxygen sensors.
• Check for any abnormal readings indicating malfunction.
• If necessary, replace the oxygen sensor that is faulty.