What Does P0174 Mean on Your 2022 Subaru WRX?
A P0174 code on your 2022 Subaru WRX indicates that Bank 2 of the FA24 2.4L turbocharged boxer engine is running too lean. This is the redesigned WRX with the new direct-injection turbo engine producing 271 horsepower, and a lean condition under boost is something you want to address quickly.
Symptoms You Might Notice
- Check engine light on or flashing
- Rough idle that may improve as the engine warms
- Noticeable power loss, especially in higher boost
- Decreased fuel economy
- Engine knock or pinging under acceleration
- Whistling or hissing from the turbo piping area
Common Causes of P0174 on the 2022 WRX
The 2022 WRX runs higher boost pressures than the Ascent, making boost leaks and fuel delivery issues even more impactful:
- Boost Leak — The turbo inlet pipe, intercooler hoses, charge pipe connections, and bypass valve are all potential leak points. Even a tiny boost leak causes significant lean conditions at high RPM.
- MAF Sensor Issues — Aftermarket intakes are common on the WRX and can contaminate the MAF sensor with excess oil. Even the stock setup can develop MAF issues.
- High-Pressure Fuel Pump Failure — The cam-driven HPFP is critical for direct injection. A weakening pump may not keep up at high RPM and boost.
- Vacuum Leak at Idle — A cracked vacuum line, leaking brake booster hose, or failed PCV valve can cause lean conditions primarily at idle.
How to Diagnose the Problem
- Scan for all codes — look for related boost, knock, or misfire codes.
- Monitor fuel trims on Bank 2 at idle and under load. LTFT above +10% confirms the problem.
- Inspect all turbo piping, intercooler connections, and the bypass valve for leaks.
- Boost leak test the entire intake tract using a pressure tester.
- Check high-pressure fuel system readings under load with an advanced scan tool.
- If running an aftermarket intake, check the MAF sensor for oil contamination.
Repair Options and Estimated Costs
- Boost leak repair: $80–$400. Clamps and silicone couplers are affordable.
- MAF sensor cleaning or replacement: $20–$280. Quick DIY fix.
- High-pressure fuel pump replacement: $500–$900 with labor.
- Vacuum line or PCV valve repair: $50–$200. Easy DIY job.
Can You Still Drive?
Drive very carefully and avoid boost. A lean condition under boost on the WRX can cause detonation, which destroys pistons, bends connecting rods, and can kill the turbocharger. This is not a code to ignore on a performance engine.
Prevention Tips
- Use premium 93 octane fuel — the WRX turbo engine demands it.
- If running aftermarket parts, ensure they are properly tuned with a professional tune.
- Inspect all boost connections regularly, especially after modifications.
- Replace the air filter on schedule and avoid over-oiling reusable filters.
- Monitor fuel trims periodically with an OBD-II scanner or AccessPort.