P0171 on a 2017 GMC Sierra 1500

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 2017 GMC Sierra 1500

Ranked from 425 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Faulty Fuel Injectors (Clogged or Failing)
High severity
Clogged or failing fuel injectors will not spray enough fuel into the cylinders, causing a lean condition. The complaints show a pattern of fuel injector failures and replacements on this specific vehicle.
Reported in 3 NHTSA complaints
2
Vacuum Leak (Intake Manifold Gasket, Vacuum Hoses, PCV System)
Medium severity
A vacuum leak introduces unmetered air into the engine, causing a lean condition. Look for cracked hoses, a hissing sound, or check fuel trims while spraying carb cleaner around the intake.
Common cause
3
Faulty or Dirty Mass Air Flow (MAF) Sensor
Medium severity
A dirty or failing MAF sensor under-reports the amount of air entering the engine, causing the PCM to provide too little fuel. Cleaning the MAF or checking its g/s reading at idle confirms this.
Common cause
4
Low Fuel Pressure (Failing Fuel Pump or Clogged Filter)
High severity
If the fuel pump is weak or the filter is clogged, the engine won't receive enough fuel to match the air intake, resulting in a lean code. Confirm by testing fuel pressure with a mechanical gauge.
Common cause
5
Exhaust Leak Before the Upstream O2 Sensor
Medium severity
An exhaust leak allows outside air to be pulled into the exhaust stream, which the O2 sensor reads as a lean condition. Look for soot marks or listen for ticking noises near the exhaust manifold.
Common cause
6
Faulty Upstream Oxygen (O2) Sensor
Low severity
A degraded or faulty upstream O2 sensor can falsely report a lean condition to the PCM. Confirm by monitoring O2 sensor voltage switching on a scan tool.
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