How to Fix a P0171 code on GM 1.4L Engines

The GM 1.4L turbo charged 4-cylinder engine, commonly found in the Chevy Sonic, Cruze and Buick Encore, has a well-known issue resulting in a lean code, P0171, and often times oil consumption and/or an engine whistle noise. This issue is often only partially repaired resulting in repeat failures. Below you’ll find the process for diagnosing and repairing the root cause resulting in a properly fixed vehicle the first time.

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Identifying symptoms and possible cause

  • Symptoms for this issue can include an engine lean condition with a P0171 code, Oil consumption and/or an engine whistle noise
  • Check if vehicle is currently experiencing any of the symptoms above
  • If the vehicle has symptoms present, test the positive crankcase ventilation (PCV) valve for a ruptured diaphragm according to testing procedure below

Testing for common PCV valve issue


Difficulty: 1/5
Time required: 5 minutes
Tools Required: Piece of paper or tissue

  1. Remove the engine cover and locate PCV valve
  1. With the engine running at idle, hold a small piece of paper or tissue in front of port. If the paper is drawn to the port, vacuum is present and the PCV valve is faulty
  1. If the PCV valve has failed, the valve cover needs to be replaced but may not be the root cause of failure. Use the test below to test for a possible root cause of PCV valve failure

Checking for root cause of PCV valve failure


Difficulty: 1/5
Time required: 10 minutes
Tools Required: Flashlight

  1. Locate and remove the PCV bypass tube from the intake manifold
  1. Using a flashlight look down the intake manifold bypass tube port and check for missing non-return valve
Tip : Oil and carbon build up may make the non-return valve dirty and harder to see
  1. Compare to photos below to determine if non-return valve is missing

Known good non-return valve (still in place)

Known bad non-return valves (missing)

P0171 Repair Procedure


Difficulty: 3/5
Time required: 2 hours
Tools Required:

Parts Required:

Intake manifold

Valve cover

RTV Silicone

PCV Bypass Tube*
*indicates if broken
  1. Remove intake manifold
Tip: An E10 Torque socket is required to remove intake manifold bolts
  1. Make sure to disconnect the small vacuum line and the wiring harness before attempting to remove the intake manifold
  1. Remove the valve cover by removing the bolts using the E10 socket
  1. Clean up all the gasket mounting surfaces making sure to remove all oil residue


  1. Apply RTV sealer to the seams where the timing cover meets the engine block
  1. Install the valve cover and torque bolts to 71 inch pounds using sequence below
  1. Swap over the throttle body, fuel rail, and map sensor to new intake manifold
Tip: Make sure to reconnect small vacuum hose and wiring harness on intake manifold
  1. Install the intake manifold and torque bolts down to 15 foot pounds
  2. Re-install all the wiring and hoses to the valve cover and the intake manifold
Tip: Check PCV bypass hose for O-ring before installing

Confirm P0171 Fix

  1. Use a small piece of paper to confirm that vacuum is no longer present at the PCV valve port
  1. If a scan tool is available, you can also monitor fuel trims and confirm they drop down to +/- 10%

For more information, questions, or help diagnosing your vehicle, contact the GoTech technical support team via phone or chat below.

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