P0171 on a 2015 Ford Escape

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 2015 Ford Escape

Ranked from 1,035 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Weak Fuel Pump / Low Fuel Pressure
High severity
A failing fuel pump cannot deliver enough fuel to match the incoming air, resulting in a lean mixture and potential stalling. Confirm by testing fuel pressure at the rail.
Reported in 1 NHTSA complaint
2
Vacuum Leak (PCV Valve or Hoses)
Medium severity
Unmetered air entering the intake manifold throws off the air-fuel ratio, causing a lean condition. Inspect PCV hoses for cracks or hissing sounds while the engine runs.
Common cause
3
Dirty or Faulty MAP/MAF Sensor
Medium severity
If the sensor incorrectly measures incoming air, the PCM will not provide enough fuel. Check sensor readings with a scan tool and clean if contaminated.
Common cause
4
Clogged Fuel Injectors
Medium severity
Restricted injectors fail to spray the commanded amount of fuel into the cylinders. Perform an injector balance test or check for localized misfires.
Common cause
5
Faulty Upstream Oxygen (O2) Sensor
Low severity
A degraded O2 sensor may falsely report a lean condition, prompting the code. Monitor the sensor's voltage switching on a scan tool to verify its responsiveness.
Common cause
6
Exhaust Leak Before O2 Sensor
Medium severity
An exhaust leak allows outside oxygen to reach the O2 sensor, tricking it into reading lean. Look for soot marks or listen for ticking noises near the exhaust manifold.
Common cause
7
Intake Manifold Gasket Leak
Medium severity
Degraded gaskets allow unmetered air to seep into the engine block. Spraying carb cleaner around the intake manifold while monitoring fuel trims will confirm the leak.
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