P0171 on a 2016 Chevrolet Malibu Eco

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 Malibu Eco

Ranked from 810 NHTSA owner complaints filed for this vehicle.

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1
Vacuum leak from failed brake-booster/vacuum pump
High severity
This pump deteriorating lets unmetered air into the intake and was directly diagnosed by mechanics/dealers as the failure point, including one case where the pump physically broke apart into the engine.
Reported in 4 NHTSA complaints
Parts:vacuum pump
2
Blown head gasket creating a vacuum/compression leak
High severity
A failed head gasket lets extra air (or combustion gas) enter the intake or exhaust path, skewing the O2 sensor's lean reading; owners reported a blown head gasket and no oil in the engine.
Reported in 2 NHTSA complaints
Parts:head gasket
3
Failing MAF/intake airflow sensor
Medium severity
An inaccurate airflow reading causes the PCM to under-fuel the engine; one owner's vehicle was diagnosed with a faulty intake airflow system.
Reported in 1 NHTSA complaint
Parts:mass airflow sensor
4
Faulty throttle body/TPS assembly
Low severity
A miscalibrated throttle position or body assembly can throw off short-term fuel trim; diagnosed as needing replacement on this vehicle.
Reported in 1 NHTSA complaint
Parts:throttle body
5
Vacuum/intake hose or gasket leaks (general)
Medium severity
Aged rubber hoses and intake gaskets crack over time and admit unmetered air; smoke-test the intake to isolate.
Common cause
Parts:vacuum hose intake manifold gasket
6
Weak fuel pump or clogged fuel filter
Medium severity
Insufficient fuel delivery pressure leans out the mixture especially under load; check fuel pressure against spec.
Common cause
Parts:fuel pump fuel filter
7
Stuck-open PCV valve
Low severity
A PCV valve stuck open acts like an unmetered vacuum leak 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