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All codes › P0171 › 2022 Toyota 4Runner

P0171 on a 2022 Toyota 4Runner

Fuel System Too Lean (Bank 1)

Severity: moderate Safe to drive (short term) Mid-size SUV 2020-2024 Toyota 4Runner

What does P0171 mean on a 2022 Toyota 4Runner?

P0171 is set when the engine control module detects that long-term fuel trim on Bank 1 has been pushed beyond approximately +25 % to compensate for what it interprets as a lean air-fuel mixture. In other words, the ECM is adding the maximum amount of fuel it is allowed to, and the oxygen sensors still report a lean condition. The cause is almost always either unmetered air entering the engine, a fuel delivery problem, or a sensor reporting bad data.

Symptoms on a 2022 Toyota 4Runner

Likely causes on a 2022 Toyota 4Runner

  1. Vacuum leak (intake manifold gasket, PCV hose, intake boot, brake booster hose) Most common
    Estimated repair: $80– $600

    The single most common P0171 cause across all makes.

  2. Dirty or failing mass airflow (MAF) sensor Most common
    Estimated repair: $30– $350

    Cleaning with MAF-safe spray solves a large fraction of cases.

  3. Weak fuel pump or clogged fuel filter (low fuel pressure) Common
    Estimated repair: $80– $900
  4. Failing fuel pressure regulator Occasional
    Estimated repair: $100– $400
  5. Clogged or leaking fuel injectors on Bank 1 Occasional
    Estimated repair: $150– $1,200
  6. Faulty oxygen sensor reporting false lean Occasional
    Estimated repair: $150– $450
  7. Exhaust leak upstream of the front O2 sensor Occasional
    Estimated repair: $100– $500

How to diagnose this on a 2022 Toyota 4Runner

  1. Read fuel trims and short-term/long-term values

    Connect a scan tool capable of live data. Compare short-term (STFT) and long-term (LTFT) fuel trims at idle and at 2500 RPM. If LTFT is +15 % or higher at idle but drops near zero at 2500 RPM, suspect a vacuum leak. If LTFT is high at all RPMs, suspect fuel delivery or MAF.

    Tools: Bidirectional scan tool with live PIDs

  2. Smoke-test the intake for vacuum leaks

    Cap the intake and introduce low-pressure smoke into the manifold. Watch for smoke escaping at intake gaskets, the PCV system, the brake booster hose, vacuum tees, and the throttle body base. Cracked plastic intake manifolds are common on many Ford, Chrysler, and Nissan engines.

    Tools: Smoke machine, Inspection mirror, Flashlight

  3. Inspect and clean the MAF sensor

    Remove the MAF sensor and spray the sensing elements with MAF-safe electronics cleaner. Reinstall, clear the code, and drive. If P0171 returns within a few drive cycles with high LTFT at cruise, the MAF may need replacement.

    Tools: MAF-safe cleaner, Trim panel tools

  4. Measure fuel pressure key-on-engine-off and at idle

    Attach a fuel pressure gauge to the fuel rail Schrader port (or use a banjo adapter on returnless systems). Compare to the OEM specification for the vehicle — most port-injected systems run 45–60 psi at idle. Pressure that drops more than 5 psi under load points to a weak pump or regulator.

    Tools: Fuel pressure gauge, Vehicle-specific service data

  5. Compare upstream O2 sensor activity to mode 6 data

    A lazy or biased O2 sensor will set P0171 even when the engine is running correctly. Graph the sensor voltage at 2500 RPM — it should switch rapidly between roughly 0.1 V and 0.9 V. If it sticks low, the sensor (not the fuel system) is the problem.

    Tools: Scan tool with graphing

Common fixes

About the 2020-2024 Toyota 4Runner

The 2020-2024 Toyota 4Runner was commonly sold with the following powertrains: 4.0L V6. Common trims include SR5, TRD Off-Road, TRD Pro, Limited.

Is P0171 dangerous to drive with?

In the short term, no. The engine will run rough and consume slightly more fuel, but the vehicle is not at immediate risk. Driving for weeks with an uncorrected lean condition is a different matter — sustained lean operation runs combustion temperatures higher than design, which can damage exhaust valves, oxygen sensors, and the catalytic converter. A car that has been driving with P0171 for months may also set P0420 as the catalyst fails.

Why P0171 often appears with P0174

P0171 covers Bank 1 (the cylinder bank containing cylinder #1) and P0174 covers Bank 2. On a V6 or V8 engine, both codes setting together rules out bank-specific causes like one injector or one head-side intake gasket. The common culprit when both banks go lean is something that affects the entire engine: a clogged MAF, a brake booster leak, low fuel pressure, or a cracked common intake plenum.

When to replace the MAF sensor vs. clean it

Cleaning resolves roughly half of MAF-related P0171 cases on high-mileage engines. Replace the MAF only if (a) cleaning does not restore correct grams-per-second airflow readings at idle, or (b) live data shows the MAF output stuck or biased low even after cleaning. A genuine OEM MAF will typically outlast a cheap aftermarket replacement by years.

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