What causes P0171 on a GMC Terrain?

Common causes of P0171 on GMC Terrain: Turbo inlet pipe seal leak on 1.5L or 2.0L turbo Equinox/Terrain causing unmetered air; PCV diaphragm failure in valve cover on 1.5T Ecotec allowing crankcase vacuum leak; MAF sensor contamination or failure on 2.4L Ecotec causing incorrect air measurement; Intake manifold gasket leak on 2.4L naturally aspirated Ecotec engine; Charge air cooler pipe clamp loosening allowing boost leak on turbo models.

P0171

P0171 GMC Terrain

Q: How much does it cost to fix P0171 on a GMC Terrain?

Fixes for P0171 on GMC Terrain include: Replace turbo inlet pipe O-ring seal and inspect all boost-side connections for leaks, Replace valve cover assembly with integrated PCV diaphragm (GM updated design), Clean MAF sensor with CRC cleaner or replace with AC Delco OE sensor, Replace intake manifold gasket set on 2.4L Ecotec and torque to specification, Tighten or replace charge air cooler pipe clamps and pressure-test boost system.

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

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 GMC Terrain 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 GMC Terrain.

This repair is rated moderate, meaning some experience and specialty tools required.

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 GMC Terrain.

Common Causes on GMC Terrain

Turbo inlet pipe seal leak on 1.5L or 2.0L turbo Equinox/Terrain causing unmetered air
PCV diaphragm failure in valve cover on 1.5T Ecotec allowing crankcase vacuum leak
MAF sensor contamination or failure on 2.4L Ecotec causing incorrect air measurement
Intake manifold gasket leak on 2.4L naturally aspirated Ecotec engine
Charge air cooler pipe clamp loosening allowing boost leak on turbo models

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 turbo inlet pipe O-ring seal and inspect all boost-side connections for leaks

Replace valve cover assembly with integrated PCV diaphragm (GM updated design)

Clean MAF sensor with CRC cleaner or replace with AC Delco OE sensor

Replace intake manifold gasket set on 2.4L Ecotec and torque to specification

Tighten or replace charge air cooler pipe clamps and pressure-test boost system

Notes for GMC Terrain

The 1.5T valve cover PCV diaphragm is a very common failure point causing P0171 on 2018+ Equinox.

P0171 GMC Terrain

What is P0171?

Common Causes on GMC Terrain

Symptoms

Notes for GMC Terrain

Check GMC Terrain Specs