P0171 on a 2021 Ram 1500 Crew Cab Trx

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 2021 Ram 1500 Crew Cab Trx

Ranked from 659 NHTSA owner complaints filed for this vehicle.

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1
Cracked exhaust manifold letting outside air reach the upstream O2 sensor
Medium severity
Multiple owners confirm cracked exhaust manifolds with leaking fumes on this truck; the extra intake air past the sensor is read by the ECU as a lean condition.
Reported in 4 NHTSA complaints
2
Weak or failing high-pressure fuel pump / fuel delivery
High severity
Recall-affected trucks in this batch stalled or lost acceleration and were traced to a failing/recalled high-pressure fuel pump, which can't maintain the pressure needed to keep the mixture in range under load.
Reported in 3 NHTSA complaints
Parts:high-pressure fuel pump fuel filter
3
Dirty or failing MAF sensor
Medium severity
An underreporting MAF causes the ECU to add less fuel than the engine actually needs; cleaning or scan-tool comparison against expected grams/sec will confirm.
Common cause
Parts:mass airflow sensor
4
Vacuum or intake air leak
Medium severity
Cracked hoses, a loose brake booster line, or a leaking intake gasket add unmetered air, the textbook cause of a bank-wide lean trim; smoke test the intake side.
Common cause
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open pulls excess crankcase air into the intake, leaning the mixture especially at idle.
Common cause
Parts:PCV valve
6
Intake manifold gasket leak
Medium severity
A failed gasket between the manifold and heads is a common unmetered-air path that produces a persistent lean code.
Common cause
Parts:intake manifold gasket

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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