P0171 on Nissan: Causes, Symptoms and Fix Cost
Quick Answer
Safe to drive (short-term)
P0171 on a Nissan means the air-fuel mixture on Bank 1 (the cylinder bank with cylinder 1) is too lean: too much air or too little fuel. The ECU keeps adding fuel to hit the 14.7:1 target ratio, but it has run out of room to compensate, so long-term fuel trim climbs past about +15% and the light comes on. The single most common cause is unmetered air entering after the airflow sensor, usually a vacuum or intake leak. Most fixes land between 100 and 350 EUR.
- Severity
- Moderate · Fuel System
- Typical repair cost, all makes
- €30-€700
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Nissan and Skanyx tells you what P0171 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0171 mean on a Nissan?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the Nissan models that log P0171.
Nissan Altima
2002-2024
On the Altima's QR25DE, P0171 most often traces to a dirty or failing mass air flow (MAF) sensor, a well-known Nissan weak point, or to an intake manifold gasket leak. The European X-Trail and Qashqai 2.0 run the MR20DE rather than the QR25DE but fail the same way. Start at the MAF: clean it first, and if it still reads low across the rev range, match the part number on the sensor you remove when you order a replacement.
What causes P0171 on a Nissan?
Beyond the generic causes listed on the main P0171 page, these are the patterns noted for Nissan models:
Dirty or failing mass air flow (MAF) sensor, a known Nissan weak point
: Nissan Altima
Intake manifold gasket or vacuum leak on the QR25DE and MR20DE
: Nissan Altima
Weak fuel pump or dirty injectors on high-mileage examples
: Nissan Altima
How to diagnose P0171 on a Nissan with OBD2
Follow these steps to pinpoint the root cause of P0171:
- Read short-term and long-term fuel trims with a scan tool. Long-term fuel trim above roughly +15% at idle confirms the lean condition, and if it improves at higher RPM the leak is unmetered air at idle
- Smoke-test the intake, or spray brake cleaner or carb cleaner around the intake manifold gasket, vacuum hoses, and PCV connections. A momentary RPM change pinpoints the leak
- Inspect and clean the MAF sensor with dedicated MAF cleaner, never touching the sensor element, then recheck fuel trims
- Check fuel pressure at the rail with a gauge and compare to the manufacturer specification, watching for pressure drop under load that points to a weak pump or clogged filter
- Inspect the PCV valve, oil separator, and their hoses for cracks, splits, or disconnection
- Check for an exhaust leak just before the upstream O2 sensor, which can fool the sensor into a false lean reading
- Compare Bank 1 and Bank 2 trims on V engines. If both banks read lean, suspect a shared cause such as the MAF, fuel supply, or a leak before the throttle body
How much does P0171 cost to fix on a Nissan? (EUR)
Estimated repair costs for P0171 in EUR, compiled across makes. Nissan costs typically sit in the middle of each range.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Fix vacuum leak (replace hose or gasket) | €5–€60 | €60–€200 | €65–€260 | Moderate |
| Clean or replace MAF sensor | €10–€200 | €20–€60 | €30–€260 | Easy |
| Replace PCV valve or oil separator | €15–€150 | €40–€180 | €55–€330 | Moderate |
| Replace fuel pump | €100–€400 | €100–€300 | €200–€700 | Professional |
| Clean fuel injectors | €15–€50 | €50–€150 | €65–€200 | Moderate |
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Codes related to P0171
These codes are often seen alongside P0171 or point to related issues, on any make:
Looking for the full P0171 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0171 guide
Diagnose P0171 on your Nissan
Your car logged P0171. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €30-€700 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.
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