P0171 on a 2017 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 2017 Ford Escape

Ranked from 2,628 NHTSA owner complaints filed for this vehicle.

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1
Coolant Intrusion into Cylinders (Cracked/Porous Engine Block)
High severity
Look for low coolant levels without external leaks, white exhaust smoke, rough idling, and misfire codes (P0301-P0304). Confirmed by cooling system pressure test and borescope inspection showing coolant in the cylinders.
Reported in 28 NHTSA complaints
2
Vacuum Leak
Medium severity
Unmetered air entering the intake manifold past the MAF sensor causes a lean condition. Look for cracked or disconnected vacuum hoses, or a leaking intake manifold gasket.
Common cause
3
Faulty 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. Confirmed by checking MAF sensor data on a scan tool.
Common cause
4
Low Fuel Pressure (Failing Fuel Pump or Clogged Filter)
Medium severity
Insufficient fuel delivery to the injectors causes a lean condition. Confirmed by testing fuel pressure with a mechanical gauge and comparing to specifications.
Common cause
5
Clogged or Faulty Fuel Injectors
Medium severity
Restricted fuel injectors fail to deliver the commanded amount of fuel, leading to a lean mixture. Confirmed by injector balance testing or observing fuel trims.
Common cause
6
Exhaust Leak Before the Upstream O2 Sensor
Medium severity
An exhaust leak allows ambient oxygen to reach the O2 sensor, falsely indicating a lean condition and causing the PCM to add fuel. Look for soot marks or listen for ticking noises near the exhaust manifold.
Common cause
7
Faulty Upstream Oxygen (O2) Sensor
Medium severity
A degraded or biased O2 sensor may falsely report a lean condition. Confirmed by monitoring sensor voltage response and fuel trim reaction on a scan tool.
Common cause
8
PCV System Leak or Faulty PCV Valve
Low severity
A stuck open PCV valve or leaking PCV hose introduces unmetered air into the intake. Confirmed by inspecting PCV hoses and testing the valve.
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