P0171 on a 2016 Chevrolet Impala Eco Eassist

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 2016 Chevrolet Impala Eco Eassist

Ranked from 786 NHTSA owner complaints filed for this vehicle.

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1
Turbocharger intake/boost hose or clamp failure
Medium severity
A complaint reports a dealer-diagnosed turbocharger clamp and exhaust/seal failure with a strong fuel-gas smell; a failed clamp on the boost side of this turbocharged engine lets unmetered air in, a documented lean-code trigger on these small-displacement turbo GM engines.
Reported in 1 NHTSA complaint
Parts:intake boost hose hose clamp
2
Rough idle/hesitation consistent with an air-fuel imbalance
Low severity
One owner's dealer visit for rough idling, hesitation, and knocking with an active check-engine light points toward an air/fuel imbalance consistent with a lean condition, though the exact leak point wasn't confirmed in the complaint.
Reported in 1 NHTSA complaint
3
Vacuum or intake manifold leak
Medium severity
Unmetered air entering downstream of the MAF sensor is the classic direct cause of a system-too-lean code.
Common cause
Parts:intake manifold gasket vacuum line
4
MAF sensor fault or contamination
Medium severity
An under-reporting MAF sensor causes the ECU to add less fuel than the engine actually needs.
Common cause
Parts:mass airflow sensor
5
Weak fuel pump or low fuel pressure
Medium severity
Falling rail pressure under load can't keep pace with injector demand, producing a lean condition most noticeable during acceleration.
Common cause
Parts:fuel pump
6
Exhaust leak upstream of the O2 sensor
Medium severity
Fresh air pulled in at a manifold or downpipe leak dilutes the exhaust sample before it reaches the upstream sensor, mimicking a lean condition.
Common cause
Parts:exhaust gasket
7
Stuck-open PCV valve
Low severity
A PCV valve that won't close draws extra unmetered crankcase air into the intake, particularly noticeable at idle.
Common cause
Parts:PCV valve

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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