P0171 on a 2018 Chevrolet Traverse
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 2018 Chevrolet Traverse
Ranked from 452 NHTSA owner complaints filed for this vehicle.
- 1
Exhaust leak from a broken/cracked exhaust pipe bracket weld
High severityWidely reported in this batch (GM TSB PIP5681A explicitly cites lean codes from a poor Bank 2 exhaust weld); the leak draws outside air in ahead of the O2 sensor.
Reported in 7 NHTSA complaints - 2
Failed or stuck-open EVAP canister purge valve/solenoid
High severityMultiple complaints document the purge valve/solenoid being diagnosed faulty and replaced (sometimes repeatedly) for drivability and CEL issues consistent with a lean condition.
Reported in 3 NHTSA complaints - 3
Vacuum leak from a failed brake-booster vacuum pump
Medium severityA complaint documents a catastrophic vacuum pump failure shedding metal debris, which is also consistent with a resulting vacuum leak feeding the intake.
Reported in 1 NHTSA complaintParts:vacuum pump - 4
Dirty or failing mass airflow (MAF) sensor
Medium severityA complaint documents a bad MAF sensor being diagnosed on this vehicle; an under-reporting MAF causes the ECU to under-fuel.
Reported in 1 NHTSA complaintParts:mass airflow sensor - 5
Intake manifold gasket leak
Low severityA leaking intake gasket admits unmetered air directly into the runners, a common source of a persistent lean code.
Common causeParts:intake manifold gasket - 6
Weak fuel pump or clogged fuel filter
Low severityInsufficient fuel delivery under load can't keep pace with airflow, producing a lean condition especially at higher RPM.
Common cause
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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.
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