P0171 on a 2013 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 2013 Ford Escape
Ranked from 2,743 NHTSA owner complaints filed for this vehicle.
- 1
Vacuum leaks (intake manifold gasket, vacuum hoses, PCV system)
Medium severityA vacuum leak introduces unmetered air into the engine, causing a lean condition. Look for cracked hoses, a hissing sound, or check fuel trims at idle versus higher RPMs.
Common cause - 2
Faulty Mass Air Flow (MAF) sensor
Medium severityA dirty or failing MAF sensor under-reports the amount of air entering the engine, leading the PCM to provide too little fuel. Confirm by cleaning the sensor or checking MAF g/s readings on a scan tool.
Common cause - 3
Low fuel pressure (failing fuel pump or clogged fuel filter)
Medium severityIf the fuel system cannot deliver adequate pressure or volume, the engine runs lean. Verify by testing fuel pressure with a mechanical gauge.
Common cause - 4
Faulty or clogged fuel injectors
Medium severityRestricted injectors fail to spray enough fuel into the cylinders, causing a lean mixture. Confirm by performing an injector balance test or checking for specific cylinder misfires.
Common cause - 5
Exhaust leaks upstream of the O2 sensor
Medium severityAn exhaust leak before the primary oxygen sensor pulls in outside air, tricking the sensor into reading a lean condition. Look for soot marks or listen for ticking noises near the exhaust manifold.
Common cause - 6
Faulty upstream Oxygen (O2) or Air/Fuel Ratio sensor
Medium severityA degraded or biased O2 sensor can falsely report a lean condition, causing the code. Confirm by monitoring sensor voltage switching or current on a scan tool.
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.
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