Rick's Free Auto Repair Advice

Equinox P0171 or Terrain P0171 trouble code

Diagnose and fix an Equinox P0171 or Terrain P0171 trouble code

If you encounter a Chevrolet Equinox P0171 or GMC Terrain P0171 trouble code, you should know that there are several issues that can cause this problem. Shops report issues with the intake manifold gasket, warped intake manifold, clogged fuel injectors and faulty MAF sensors. Aside from getting the code, your first step should to attach a scan tool and check for fuel trims.

Fuel trims and Equinox P0171 or Terrain P0171 trouble code

A P0171 FUEL METERING TOO LEAN code can mean the engine is getting too much unmetered air or too little fuel. So you want to see if the PCM is trying to add fuel. Refer to the short and long term fuel trim data on your scan tool. Short term fuel trims should vary as your drive the vehicle. GM states that the normal short term fuel trims are between +10% and -10%, with 0% as the optimal reading. These values are measured with the engine at full operating temperature. Normal long term fuel  values should also be between +10% and -10%, with 0% as the optimal reading.

If the readings you see are above 10%, the PCM is adding fuel to compensate for unmetered air or low fuel. Low fuel can be caused by low fuel pressure or low fuel volume, clogged fuel filter or clogged injectors.

Check air intake

Aftermarket air filters, aftermarket cold air intakes and aftermarket exhaust systems

A bad or dirty maf sensor can cause a high idle

A mass airflow sensor detects the amount and density of air coming into the engine

can drastically modify MAF sensor readings, creating an Equinox P0171 or Terrain P0171 trouble code. So check the air filter first. Next, check the reading for the MAF sensor. Check reference, ground and signal. A wildly erratic signal can be the sign of a faulty MAF sensor. Clean the MAF sensor (click here for the cleaning procedure). If the air intake and MAF check out, move on to fuel.

Check for intake manifold leaks and leaking vacuum lines

Any air that enters the engine after the MAF system is unmetered air. A disconnected vacuum line, leaking intake manifold gasket or warped intake manifold (they’re plastic and can warp) can allow unmetered air into the engine. Check all vacuum line connections.

equinox P0171

Equinox/Terrain Intake Manifold

Connect your scan tool or scope to watch Oxygen sensor reading while you perform a propane enrichment test. Using a propane torch, add propane fuel around the intake manifold, exercising proper care to avoid ignition. Watch the O2 sensor readings while you do this. If the O2 readings spike, you’ve found an air leak.

If the above tests don’t detect unmetered air, conduct a smoke test.

Check fuel pressure and delivery

Attach a fuel pressure gauge and check fuel pressure with the engine running and during a test drive. If the fuel pump delivers the proper fuel and volume,

If nothing else solves the problem, clean the fuel injectors.

Other possibilities for a Equinox P0171 or Terrain P0171 trouble code include a faulty EGR valve that’s allowing either exhaust or ambient air into the engine.

©, 2018 Rick Muscoplat

Posted on by Rick Muscoplat

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