P0171 on a 2020 Toyota Rav4

P0171 means the engine computer is adding more fuel than normal on bank 1 because it sees too much air or not enough fuel.

Not your vehicle? See general P0171 info.

Most common causes on the 2020 Toyota Rav4

Ranked from 627 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Weak or failing fuel pump
High severity
One owner's engine stalled while fueling and would not restart, diagnosed as a fuel pump failure; inadequate fuel delivery under demand is a direct cause of a lean fuel trim code.
Reported in 1 NHTSA complaint
Parts:fuel pump
2
Low fuel pressure sensor fault (hybrid fuel system)
Medium severity
One owner had the low fuel pressure sensor replaced after a hybrid-system malfunction with power loss on the highway; an inaccurate low-pressure reading can cause the system to under-deliver fuel, producing a lean condition.
Reported in 1 NHTSA complaint
Parts:fuel pressure sensor
3
Vacuum or intake leak
Medium severity
Unmetered air entering after the mass airflow sensor (cracked hose, loose intake boot, leaking gasket) directly causes a lean fuel trim code.
Common cause
4
Dirty or failing mass airflow (MAF) sensor
Medium severity
A contaminated or drifting MAF sensor under-reports incoming air, causing the PCM to under-fuel and trip a lean code.
Common cause
Parts:mass airflow sensor
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open draws excess unmetered air into the intake, leaning the mixture, especially at idle.
Common cause
Parts:PCV valve
6
Exhaust leak upstream of the upstream O2 sensor
Low severity
A leak ahead of the front oxygen sensor draws in outside air the sensor reads as excess oxygen, causing the PCM to lean the mixture further.
Common cause
7
Intake manifold gasket leak
Low severity
A failed intake gasket is a common unmetered-air path that produces a steady lean condition.
Common cause
Parts:intake manifold gasket

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0171 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Rough idle
Hesitation
Surging idle
Poor fuel economy

What to check before replacing parts

Review short- and long-term fuel trims on bank 1

Look for: High positive trims (commonly worse at idle, improving with RPM) mean the computer is adding fuel to compensate for excess air or insufficient fuel — that pattern is this code's fingerprint.

Smoke-test the intake

Look for: Smoke escaping (or a hiss you can hear) at intake boots, gaskets, or vacuum hose connections confirms unmetered air is entering after the MAF sensor, which is the most common cause of a lean code.

Inspect the PCV hoses and valve

Look for: A cracked, split, or disconnected PCV hose, or a PCV valve stuck open, draws in extra unmetered air the same way a vacuum leak does.

Clean and test the MAF sensor

Look for: Visible dirt or oil film on the sensor element, or a grams/second reading that doesn't track expected airflow for RPM, means the MAF is under-reporting air and causing the computer to under-fuel.

Verify fuel pressure

Look for: Pressure below spec (weak pump, clogged filter, failing regulator) starves the engine of fuel and produces the same lean trim pattern as a vacuum leak — rule it out before chasing leaks.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Car Runs Rough