P0171 on Subaru: System Too Lean (Bank 1)
Severity: 2 of 4
Usually drivable in the short term if the car runs well and the light is steady. Get it fixed soon, because a lean engine can misfire and run hot. If you get misfire codes or the light flashes, park it.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0171 usually means on a Subaru
Subaru lean codes often trace to the MAF sensor or air leaks in the intake ducting. Subaru engines are sensitive to unmetered air, so even a loose clamp can trigger the code.
Most likely causes on Subaru vehicles
- Dirty MAF sensor
- Loose intake boot or clamp
- PCV hose
- Fuel pressure
Order reflects cost and likelihood in general; your vehicle may differ. Confirm with testing before buying parts.
Subaru specific tips
- Clean the MAF and inspect the intake boot first.
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Vacuum or PCV hose | $10 to $80 | 0.3 to 1.0 h | $10 + 0.3 × $110 = $43 $80 + 1.0 × $190 = $270 |
| MAF sensor cleaning or replacement | $10 to $250 | 0.2 to 0.5 h | $10 + 0.2 × $110 = $32 $250 + 0.5 × $190 = $345 |
| Intake manifold gasket | $20 to $150 | 1.0 to 4.0 h | $20 + 1.0 × $110 = $130 $150 + 4.0 × $190 = $910 |
| Fuel pump | $120 to $600 | 1.5 to 3.5 h | $120 + 1.5 × $110 = $285 $600 + 3.5 × $190 = $1,265 |
Costs are generic for this code; parts and labor on some Subaru models may run higher.
Watch a repair video
System Too Lean: Code P0171 or P0174 (1A Auto). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0171 Subaru fix” videos.
Repair manuals
Step-by-step service manuals for Subaru with torque specs and wiring diagrams:
Haynes manuals for Subaru Chilton manuals
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Check Subaru recalls
Enter your VIN at the NHTSA recall lookup before paying for repairs.
FAQ
Can an oiled aftermarket air filter cause P0171 on a Subaru?
Yes, over oiled filters can contaminate the MAF sensor.
Read the full P0171 guide or more Subaru check engine notes.