What causes P0171 on a Nissan Altima?

Common causes of P0171 on Nissan Altima: Intake manifold gasket leak on QR25DE Altima from thermal cycling and age; MAF sensor contamination or failure on QR25DE or MR20DD (Altima/Sentra); PCV valve failure on QR25DE causing crankcase vacuum leak; Cracked intake air hose between MAF sensor and throttle body on Sentra; Fuel injector partial clogging reducing fuel delivery on one or more cylinders.

P0171

P0171 Nissan Altima

Q: How much does it cost to fix P0171 on a Nissan Altima?

Fixes for P0171 on Nissan Altima include: Replace intake manifold gasket with Nissan OE or Fel-Pro aftermarket set, Clean MAF sensor with CRC cleaner or replace with Hitachi OE on QR25DE, Replace PCV valve and connecting hose with Nissan OE parts, Replace cracked intake air hose and inspect all connections for air leaks, Clean fuel injectors with professional ultrasonic service or replace clogged units.

System Too Lean (Bank 1) · Powertrain Code · High · Repair: Easy

What is P0171?

The engine is running lean on bank 1 — too much air or not enough fuel. Common causes include vacuum leaks, weak fuel pump, clogged fuel injectors, or a faulty MAF sensor.

When the Nissan Altima triggers code P0171 (system too lean (bank 1)), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the Nissan Altima.

This repair is rated easy, meaning basic tools, no lift needed.

Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Nissan Altima.

Common Causes on Nissan Altima

Intake manifold gasket leak on QR25DE Altima from thermal cycling and age
MAF sensor contamination or failure on QR25DE or MR20DD (Altima/Sentra)
PCV valve failure on QR25DE causing crankcase vacuum leak
Cracked intake air hose between MAF sensor and throttle body on Sentra
Fuel injector partial clogging reducing fuel delivery on one or more cylinders

Symptoms

Rough or unstable idle speed
Hesitation or stumble during acceleration
Engine surging or hunting at idle
Lean misfire under load causing jerking
Poor acceleration response and reduced power
Check engine light illuminated

Recommended Fixes

Replace intake manifold gasket with Nissan OE or Fel-Pro aftermarket set

Clean MAF sensor with CRC cleaner or replace with Hitachi OE on QR25DE

Replace PCV valve and connecting hose with Nissan OE parts

Replace cracked intake air hose and inspect all connections for air leaks

Clean fuel injectors with professional ultrasonic service or replace clogged units

Notes for Nissan Altima

The QR25DE intake manifold gasket is a common lean-code cause on Altima; relatively inexpensive repair.

P0171 Nissan Altima

What is P0171?

Common Causes on Nissan Altima

Symptoms

Notes for Nissan Altima

Check Nissan Altima Specs