P0171 on a 2020 Acura Rdx

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 2020 Acura Rdx

Ranked from 339 NHTSA owner complaints filed for this vehicle.

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1
Turbocharger/intercooler moisture intrusion disrupting intake air metering
High severity
A large cluster of owners describe sudden limp mode with the check-engine light flashing during rain/humid weather, consistent with water in the intake tract confusing airflow measurement and skewing fuel trim lean.
Reported in 11 NHTSA complaints
Parts:intercooler
2
Failing in-tank fuel pump (NHTSA Recall 23V-858)
High severity
Several owners report fuel-pump failure explicitly tied to NHTSA Recall 23V-858, with symptoms of stalling, failure to start, and sudden loss of power consistent with inadequate fuel delivery/pressure that would drive a lean trim.
Reported in 5 NHTSA complaints
Parts:fuel pump
3
Vacuum or intake air leak
Medium severity
Unmetered air entering downstream of the MAF sensor is the classic P0171 cause; smoke-test intake boots, hoses, and gaskets.
Common cause
4
Dirty or failing mass airflow (MAF) sensor
Medium severity
A contaminated or drifting MAF under-reports intake air, making the ECU add less fuel than needed.
Common cause
Parts:mass airflow sensor
5
Stuck-open PCV valve
Low severity
Excess unmetered crankcase air pulled through a stuck-open PCV valve skews the fuel trim lean.
Common cause
6
Intake manifold gasket leak
Medium severity
A leaking manifold gasket is a common chronic vacuum-leak source producing a persistent lean code.
Common cause
7
Exhaust leak upstream of the front oxygen sensor
Low severity
A leak ahead of the upstream O2 sensor draws in outside air and falsely reads lean.
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.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Car Runs Rough