Honda-specific code — factory diagnostic data| DTC Data Sheet | |
| Code | P0171 |
| Vehicle | Honda Civic (2006-2024) |
| Engine | 1.8L R18 / 2.0L K20 / 2.4L K24 |
| System | FUEL AND AIR METERING |
| Fault type | Performance |
| Official meaning | System Too Lean (Bank 1) |
Definition source: Honda factory description. Diagnostic guidance is based on factory-defined fault logic for this code.
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Looking for the cross-vehicle definition? Read the generic P0171 article for the SAE-defined fault logic that applies to all manufacturers.
P0171 Quick Answer
P0171 on a Honda Civic is typically caused by a PCV valve failure (Civic-specific common pattern), MAF sensor contamination, or an intake manifold gasket leak — especially on the 8th-gen 1.8L R18 (2006-2011) where the intake gasket is a known weak point. Less common: dirty fuel injectors or a clogged fuel filter on older fuel-pump-equipped Civics.
What Does P0171 Mean on a Honda Civic?
The Honda Civic (2006-2024) stores P0171 when the condition described above is met. The model-specific failure patterns documented below apply to the Civic’s engine family and differ from the generic SAE definition.
Symptoms
- Check Engine Light (P0171)
- Rough idle, smooths above 1500 RPM
- Hesitation on tip-in from stop
- Slight fuel economy loss
- Possible P0300 misfire as condition worsens
Common Causes (Most Likely on This Model First)
- Failed PCV valve. Civic-specific high-frequency cause. The PCV valve on the K-series is at the back of the head and gets neglected. A stuck-open valve creates an excessive vacuum leak; stuck-closed builds crankcase pressure. Cheap part, easy job.
- MAF sensor contamination. Honda MAFs collect oil mist from blow-by. Clean with CRC MAF-specific cleaner (never carb cleaner).
- Intake manifold gasket leak (8th-gen 1.8L R18). Documented weak point. The rubber gasket between intake runner and head hardens after 100k+ miles.
- Vacuum line crack at brake booster. The molded hose develops cracks where it bends. Inspect carefully.
- Failing fuel injector. Less common but a partially-clogged injector causes a cylinder-specific lean issue that the PCM compensates for by enriching the bank.
- Worn O2 sensor (Bank 1 Sensor 1). Slow upstream sensor mis-reports mixture. Honda O2 sensors are good for 100k-120k miles.
Diagnostic Approach
- Read freeze frame, note LTFT B1. > +15% is significant.
- Inspect PCV valve and hose on K-series and R18 engines. Cheap and easy first check.
- Clean MAF sensor with CRC MAF cleaner. Drive 50 miles, recheck fuel trims.
- Smoke-test the intake. Pay attention to the intake gasket on 8th-gen 1.8L Civics.
- Inspect brake booster hose for cracks.
- Check upstream O2 sensor response time on a scan tool — slow switching = sensor wearing.
Possible Fixes
| Fix | When |
|---|---|
| Replace PCV valve | Always first on Civics — cheap and common fix |
| Clean MAF sensor | MAF contaminated |
| Replace intake manifold gasket | 8th-gen 1.8L, smoke test confirms |
| Replace upstream O2 sensor | O2 > 100k miles, slow response |
| Replace brake booster hose | Cracks visible |
Can I Still Drive With P0171?
Yes short-term. Extended lean operation damages the catalyst eventually — fix within a few weeks.
How Serious Is This Code?
Moderate. Lean condition compounds (P0420 eventually appears if ignored).
Repair Costs
| Repair | Cost |
|---|---|
| PCV valve replacement | $40 – $120 |
| MAF cleaning (DIY) | $10 |
| MAF sensor replacement | $140 – $280 |
| Intake manifold gasket | $380 – $680 |
| Upstream O2 sensor | $160 – $280 |
FAQ
What is the most common cause of P0171 on a Honda Civic?
On Civics specifically, the PCV valve is a high-frequency cause — much more often than on other brands. Always check the PCV valve and hose first. MAF contamination is second. Intake manifold gasket leak is common on the 8th-gen 1.8L R18.
How much to fix P0171 on a Honda Civic?
PCV valve: $40-$120 (cheapest fix, and common). MAF cleaning: $10. MAF replacement: $140-$280. Intake gasket: $380-$680. Most Civic P0171 cases resolve in the $10-$200 range.
Will P0171 cause damage on a Civic?
Extended lean operation eventually overheats the catalytic converter. P0420 (cat efficiency) typically appears after months of unaddressed P0171. Fix the lean condition early to avoid cat replacement later.
Can I drive my Civic with P0171?
Yes — short-term. The engine runs slightly lean and may idle rough, but it won’t leave you stranded. Address within a few weeks to prevent cat damage.