P0171 on a 2013 Toyota Camry

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 2013 Toyota Camry

Ranked from 301 NHTSA owner complaints filed for this vehicle.

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1
Vacuum Leak (Intake Manifold Gasket, Vacuum Hoses, PCV)
Medium severity
A vacuum leak introduces unmetered air into the engine, causing a lean condition. Look for cracked or disconnected vacuum hoses, a faulty PCV valve, or a leaking intake manifold gasket.
Common cause
2
Faulty Mass Air Flow (MAF) Sensor
Medium severity
A dirty or failing MAF sensor will incorrectly measure the amount of air entering the engine, leading the ECM to under-fuel the engine. Cleaning or replacing the MAF sensor often resolves this.
Common cause
3
Low Fuel Pressure (Failing Fuel Pump or Clogged Filter)
Medium severity
If the fuel pump is weak or the fuel filter is clogged, the engine will not receive enough fuel to match the incoming air, resulting in a lean code. Confirm by testing fuel pressure at the rail.
Common cause
4
Faulty Oxygen (O2) Sensor or Air/Fuel Ratio Sensor
Medium severity
A degraded upstream air/fuel ratio sensor or downstream O2 sensor can falsely report a lean condition or fail to properly regulate the fuel mixture. Diagnosis involves checking sensor voltage and response times.
Common cause
5
Clogged or Dirty Fuel Injectors
Medium severity
Restricted fuel injectors will not spray the commanded amount of fuel into the cylinders, causing a lean mixture. This can be confirmed by injector balance testing or observing fuel trims.
Common cause
6
Exhaust Leak Before the O2 Sensor
Medium severity
An exhaust leak upstream of the primary oxygen sensor can draw in outside air, tricking the sensor into reading a lean condition and triggering the code. Inspect the exhaust manifold and downpipe for soot or cracks.
Common cause

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