how to fix the P0171 lean condition code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the battery to avoid electrical shorts during the process.

2. Inspect and Repair Air Intake System

• Sub-steps:
  1. Visually inspect all intake hoses and connections for cracks or leaks. Replace any damaged components.
  2. Remove the air filter and inspect it for dirt and blockage. Replace if necessary.
  3. Check the MAF sensor; if dirty, clean it with MAF sensor cleaner. Ensure no residue remains.

Tools Required: Screwdrivers, Pliers, MAF sensor cleaner

3. Check Fuel System

• Sub-steps:
  1. Connect the fuel pressure gauge to the fuel rail and turn the ignition on (do not start the engine).
  2. Check the fuel pressure; it should be within the specifications (typically around 40-50 PSI for most Toyota engines).
  3. If pressure is low, inspect the fuel pump and fuel filter for issues. Replace the fuel filter if clogged.
  4. Inspect fuel injectors for proper operation; clean or replace as necessary.

Tools Required: Fuel pressure gauge, socket set, fuel injector cleaner

4. Inspect Engine Coolant Temperature Sensor (if applicable)

• Sub-steps:
  1. Locate the engine coolant temperature sensor.
  2. Disconnect the sensor connector and check resistance with a multimeter; refer to service manual for specific values.
  3. Replace the sensor if it does not meet specifications.

Tools Required: Multimeter, socket set