how to fix P0171 code causing lean condition in GMC Sierra T1XX (2019-Present)

Learn how to diagnose and fix P0171 fuel system lean condition in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required: OBD-II scanner, vacuum gauge, fuel pressure gauge, multimeter, basic hand tools (sockets, wrenches).
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect for Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  • Use a vacuum gauge to check for leaks; a reading significantly lower than expected indicates a leak.
  • If leaks are found, replace damaged hoses or gaskets.

3. Check Fuel Pressure

• Sub-steps:
  • Locate the fuel pressure test port on the fuel rail.
  • Attach the fuel pressure gauge and turn the ignition on (do not start the engine).
  • Compare the reading to the manufacturer's specifications (typically around 55-62 psi for most GM vehicles).
  • If pressure is low, inspect the fuel pump, filter, and lines for blockages or failures.

4. Inspect and Clean the MAF Sensor

• Sub-steps:
  • Locate the MAF sensor in the intake air duct.
  • Disconnect the electrical connector and remove the sensor from the duct.
  • Use MAF sensor cleaner to gently clean the sensor; avoid touching the sensor wires.
  • Reinstall the MAF sensor and reconnect the electrical connector.

5. Test Fuel Injectors

• Sub-steps:
  • With the engine off, disconnect the fuel injector connectors.
  • Use a multimeter to check the resistance of each injector (should be within manufacturer specs, usually around 12-16 ohms).
  • If an injector is out of spec, replace the faulty injector.

6. Replace Oxygen Sensors (if necessary)

• Sub-steps:
  • If any oxygen sensors are found to be malfunctioning during diagnostics, replace them.
  • Use an O2 sensor socket to remove the old sensor and install the new one.
  • Ensure proper torque specifications for installation (generally around 30 lb-ft).