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.Article contents
- Identifying symptoms and possible cause
- Testing for common PCV valve issue
- Checking for root cause of PCV failure
- P0171 repair procedure
- Confirm P0171 fix
Identifying symptoms and possible cause
Watch- 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
WatchDifficulty: 1/5
Time required: 5 minutes
Tools Required: Piece of paper or tissue
- Remove the engine cover and locate PCV valve

- 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

- 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
WatchDifficulty: 1/5
Time required: 10 minutes
Tools Required: Flashlight
- Locate and remove the PCV bypass tube from the intake manifold

- 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

- 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
WatchDifficulty: 3/5
Time required: 2 hours
Tools Required:
Parts Required:
| Valve cover | RTV Silicone | PCV Bypass Tube* |
- Remove intake manifold
Tip: An E10 Torque socket is required to remove intake manifold bolts

- Make sure to disconnect the small vacuum line and the wiring harness before attempting to remove the intake manifold


- Remove the valve cover by removing the bolts using the E10 socket

- Clean up all the gasket mounting surfaces making sure to remove all oil residue
Installation
- Apply RTV sealer to the seams where the timing cover meets the engine block

- Install the valve cover and torque bolts to 71 inch pounds using sequence below

- 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
- Install the intake manifold and torque bolts down to 15 foot pounds
- 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
Watch- Use a small piece of paper to confirm that vacuum is no longer present at the PCV valve port

- 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.