P0171 on a 2019 Chevrolet Malibu

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 2019 Chevrolet Malibu

Ranked from 188 NHTSA owner complaints filed for this vehicle.

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1
Charge-Air Hose / Throttle Body Hose Disconnection
High severity
The charge-air hose blows off the throttle body due to missing/broken retention clips or gaskets, causing a massive unmetered air leak and sudden loss of power.
Reported in 2 NHTSA complaints
2
Clogged or Failing Fuel Injectors
Medium severity
Restricted fuel injectors cannot deliver the commanded amount of fuel, leading to a lean mixture. Confirmed by an injector balance test or observing misfires on specific cylinders.
Reported in 1 NHTSA complaint
3
Vacuum Leak (Intake Manifold, PCV, or Vacuum Hoses)
Medium severity
Unmetered air entering the engine leans out the air/fuel mixture. Look for cracked hoses, a hissing sound, or high fuel trim readings at idle that improve at higher RPMs.
Common cause
4
Faulty Mass Air Flow (MAF) Sensor
Medium severity
A dirty or failing MAF sensor under-reports the amount of air entering the engine, causing the ECM to inject less fuel. Confirmed by checking MAF g/s readings on a scan tool.
Common cause
5
Low Fuel Pressure (Failing Fuel Pump or Clogged Filter)
High severity
Insufficient fuel delivery causes a lean condition. Confirmed by testing fuel pressure with a mechanical gauge and comparing it to specifications.
Common cause
6
Faulty Oxygen (O2) Sensor (Upstream)
Low severity
A degraded or biased upstream O2 sensor can falsely report a lean condition, causing the ECM to set P0171. Confirmed by observing sluggish or biased O2 sensor voltage graphs.
Common cause
7
Exhaust Leak Before the Upstream O2 Sensor
Medium severity
An exhaust leak allows outside oxygen to enter the exhaust stream, tricking the O2 sensor into reading lean. Look for soot marks or listen for ticking noises near the exhaust manifold.
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