P0172 Code: Honda Civic (2022-2024) - Causes, Symptoms & Fixes

Below is a comprehensive diagnostic guide for OBD-II code P0172 on the 2022–2024 Honda Civic. Note on data limits: Based on the provided NHTSA data snippet, there are no owner complaints or recalls listed for this combination. No recalls found in NHTSA database. The guide that follows combines the code meaning, Honda-specific typical failure modes, symptom patterns, step-by-step diagnostics, repair options with 2025 price ranges, DIY vs professional considerations, and prevention tips. Data limitations are acknowledged where relevant.

CODE MEANING AND SEVERITY

• Meaning: P0172 = System Too Rich (Bank 1). For a 4-cylinder Honda Civic (2022–2024), Bank 1 is the only bank. The PCM (engine control module) has detected a long-term fuel trim that is too rich for Bank 1, indicating more fuel is being added than the ECM thinks is necessary, over an extended period.
• Severity and impact:
  • MIL (Check Engine Light) is usually illuminated.
  • Symptoms may include reduced throttle response, rough idle, and diminished performance.
  • Potential long-term risk if unresolved: catalyst damage from rich exhaust, fouled plugs, increased fuel consumption, and pressure on the fuel system.
• Important note: P0172 can be triggered by several issues that cause the ECU to compensate with extra fuel or by sensor misreadings. Diagnosis should verify the actual fuel trim values and correlate with other diagnostic data.

COMMON CAUSES ON THE HONDA CIVIC (2022–2024)

These are typical sources that can lead to a P0172 condition on Civics with the 1.5L turbo (the common Civic engine for these model years). Prioritize checking for issues that affect fueling, air measurement, and exhaust readings.

• Dirty or faulty MAF sensor (air mass flow sensor) or related wiring
  • A dirty or failing MAF can cause the ECU to miscalculate air, prompting excess fuel delivery.
• Air intake issues
  • Dirty/blocked air filter, collapsed intake duct, loose or cracked intake hoses, or leaks after the MAF can cause improper air measurement.
• Vacuum leaks (especially around PCV system and intake plumbing)
  • While vacuum leaks more commonly cause lean conditions (P0171), complex interactions with turbocharged engines and sensor readings can contribute to a rich trim under certain operating conditions.
• Faulty or slow-response upstream O2 sensor (HO2S) or downstream O2 sensor
  • A defective sensor can misreport exhaust gas composition, causing improper fuel trim adjustments.
• Faulty fuel delivery or fuel pressure regulation
  • High fuel pressure or injector-specific issues can push more fuel into the cylinders than desired.
• Leaking or sticking fuel injectors
  • Leaking or partially stuck injectors can flood a cylinder or the intake, triggering a rich condition.
• Faulty coolant temperature sensor (ECT) or sensor harness
  • If the ECU misreads engine temperature, it may enrich fuel when the engine is not warming properly.
• Faulty or dirty EGR system (if equipped) or related plumbing
  • EGR flow issues can affect fuel trims and sensor readings.
• Fuel trim memory corruption or ECU calibration issue
  • In rare cases, software/ECU faults may contribute to abnormal long-term fuel trims.
• Faulty or degraded fuel pump/fuel pump relay or pressure regulator (in-tank rail regulators)
  • Abnormal rail pressure can alter actual vs. commanded air-fuel mixture.
• Carbon buildup on intake valves (direct-injection engines)
  • In direct-injection Civics, carbon buildup can affect cylinder airflow and sensor readings, influencing fuel trim behavior.
• Wiring harness or connector problems (corrosion, loose connections)
  • Sensor readings and actuator behavior rely on good electrical connections.

SYMPTOMS TO EXPECT

• Check Engine Light (MIL) is on or flashing.
• Engine runs noticeably rich: strong petrol smell, black exhaust soot, or sooty spark plugs over time.
• Reduced fuel economy due to excess fuel consumption.
• Rough idle, hesitation, or misfires under certain conditions (especially at idle or light load).
• Possible exhaust smell (gasoline) in the cabin or near the exhaust.
• Possible catalytic converter heating or performance concerns if the condition persists.

DIAGNOSTIC STEPS (step-by-step)

Tools you’ll want:

• OBD-II scan tool with live data and freeze-frame capabilities
• Multimeter (for sensor testing as needed)
• Fuel pressure gauge (for rail pressure check)
• Noid light or oscilloscope for injector testing (optional but helpful)
• MAF cleaner (for cleaning if dirty)
• Basic hand tools

A. Confirm and scope the fault

• Retrieve DTC P0172 with ignition on and engine running; note any related codes (P0171, P0174, P013x, P013x, P0139, P0130, etc.).
• Review freeze-frame data: LTFT (Long Term Fuel Trim) for Bank 1; STFT (Short Term Fuel Trim) at idle and at a fast idle or part-throttle. Note values, current MAF reading, coolant temperature, engine RPM, and fuel trim history.
• If LTFT is high (e.g., +15% to +40% or higher for Bank 1), focus on ingredients that add fuel or misread air.

B. Perform a thorough visual and mechanical inspection

• Inspect for obvious vacuum leaks around the intake, PCV valve, hoses, gaskets, and the turbocharger intercooler plumbing (if applicable).
• Check air intake path: air filter condition, intake duct seals, throttle body gasket, and any aftermarket modifications.
• Inspect fuel system for signs of leakage or corrosion; verify there are no signs of fuel odor around engine bay.

C. Inspect and test the MAF sensor

• Remove and inspect MAF sensor for contamination; clean with appropriate MAF sensor cleaner if dirty (do not use an aggressive cleaner).
• Reinstall and recheck live data: compare MAF values to expected ranges at idle and at higher engine speeds. If readings are abnormally high or low and cleaning did not help, replace MAF sensor.
• Check MAF sensor voltage/ground wiring for continuity and proper resistance as per service manual.

D. Check the MAP sensor and air measurement sensors

• If the Civic uses a MAP sensor in addition to MAF, verify MAP sensor readings at idle and under boost to ensure they respond correctly.
• Look for symptoms of a faulty MAP or wiring: high resistance, poor grounding, or intermittent signals.

E. Test the O2 sensors (HO2S)

• Inspect upstream O2 sensor readings (before catalytic converter). If the sensor is slow to respond or reads almost always rich/lean abnormally, test or replace as needed.
• Confirm the downstream O2 sensor readings (post-cat) are not giving misleading data; a damaged downstream sensor can cause PCM to misinterpret catalytic efficiency and alter fuel trim.

F. Check fuel delivery and pressure

• Perform a static fuel pressure test and compare to manufacturer's specification (service manual for exact values). If pressure is too high, regulator/fuel rail issues may be present; if too low, pump or filter/flow limitations could contribute to inconsistent fueling.
• If you can, perform a dynamic fuel pressure test during engine operation to observe how pressure changes with load.
• If possible, perform injector balance/flow test or listen for stuck-open injectors with a mechanic’s stethoscope or use a noid light to confirm injector firing. A leaking or stuck injector can create a rich condition.

G. Inspect the cooling and temperature sensors

• Check the coolant temperature sensor reading in live data. If the engine temp appears to read cold or unduly warm relative to actual temperature, this can cause improper fueling decisions.
• Verify ECT sensor wiring for proper resistance and grounding.

H. Evaluate the EGR system (if equipped)

• Ensure EGR valve operation is correct and that passages are not clogged. An EGR fault can affect mixture readings and fuel trims.

I. Look for related mechanical issues

• Carbon buildup on intake valves (especially on direct-injection Civics) can influence air flow and sensor readings; assess if a carbon cleaning is indicated by symptoms and code behavior.
• Inspect for exhaust leaks before the O2 sensors; a leak can cause false readings and mislead fuel trim data.

J. Additional considerations

• If all components test good but problem persists, consider ECU/software update or reflash (as per Honda service advisories). In rare cases, PCM faults can manifest as abnormal fuel trim behavior.

RELATED CODES

• P0171: System Too Rich? No, typically “System Too Lean (Bank 1)” is P0171. Depending on vehicle generation, both P0171 and P0172 can appear in the same scan scenario if a systemic sensor misread causes both sides to swing.
• P0174: System Too Lean (Bank 2) — relevant if you have more than one bank or if a shared sensor or wiring issue affects multiple banks.
• P013x/P013x: O2 sensor circuit-related codes (upstream or downstream, depending on the bank and sensor location).
• P0101: MAF sensor circuit range/performance.
• P219x: O2 sensor signal stuck rich/lean (if a sensor itself is faulty).
• P0300/P0301-P0304: Random or cylinder-specific misfire codes that may accompany a rich condition due to misfiring or fuel settings.

REPAIR OPTIONS AND COSTS (2025 PRICING)

Prices vary by region, labor rates, and exact parts used. The ranges below are typical for the U.S. market in 2025 and assume standard, mid-range parts. All prices are ballpark estimates for parts plus labor; shop labor may be higher in some regions.

Low-cost/DIY-friendly fixes (rough ranges; DIY saves labor):

• MAF sensor cleaning or replacement
  • Cleaning: often free if you do it yourself (~$0 for cleaner; time investment).
  • MAF replacement (OEM or aftermarket): $120–$350 parts; labor if done by you: $0; if done by shop: $60–$150.
• Air filter replacement and intake cleaning
  • Air filter: $10–$30; DIY labor: $0; shop: $30–$60.
  • Throttle body cleaning (if needed): $50–$120 parts, $60–$150 labor if done by shop.
• PCV valve and hose replacement
  • PCV valve: $5–$25; hoses: $20–$60; labor: $40–$100.
• Vacuum line/check valve replacements
  • Hoses and check valves: $20–$80 parts; labor: $40–$120.
• O2 sensor replacement (upstream) if easy to access
  • Sensor: $40–$150 for aftermarket; $100–$250 for OEM; labor: $60–$150.

Moderate repairs (often DIY with guidance, or medium-shop work):

• Upstream O2 sensor replacement (correct type for Bank 1)
  • Parts: $80–$250; labor: $60–$180.
• Fuel pressure regulator/fuel rail components or fuel injectors (service/diagnosis, not full replacement)
  • Regulator or related rail components: $50–$250 parts; labor: $100–$250.
  • Fuel injectors (service1 or replacement kit): cleaning kit or service: $50–$100; replacement per injector when replacing all four: $120–$400 (parts) plus $150–$350 labor for a full set.

Expensive repairs (professional, often necessary):

• Fuel pump replacement
  • Parts: $150–$600; labor: $200–$600.
• Injectors (full replacement or replacement set with re-seating)
  • Parts: $300–$800 (set of four for OEM or reputable aftermarket); labor: $250–$600.
• EGR valve replacement
  • Parts: $80–$350; labor: $100–$250.
• Intake manifold gasket or plenum gasket replacement
  • Parts: $50–$200; labor: $200–$600.
• Throttle body replacement
  • Parts: $150–$500; labor: $100–$250.
• PCM/ECU repair or replacement
  • Parts: $600–$1,400 (plus potential programming); labor: $150–$400.
• Catalyst-related restrictions or catalytic converter replacement
  • Parts: $600–$1,800+; labor: $200–$1,000+ (depends on location and exhaust system)
• Major software/ECU reflash or update (dealer required)
  • Service: $0–$250 (often included with a larger repair); ECU programming fees may apply.

Notes:

• Prices are indicative and can vary widely by location, dealer vs independent shop, and availability of OEM vs aftermarket parts.
• If multiple issues are found (e.g., MAF dirty + clogged injector), combined repairs may be cost-effective.

DIY VS PROFESSIONAL

• DIY-priority candidates:
  • Cleaning or replacing the MAF sensor (with proper cleaner and precautions).
  • Replacing the air filter and PCV valve.
  • Replacing cracked vacuum hoses or PCV lines.
  • Basic O2 sensor checks with a scan tool and basic electrical checks.
  • Cleaning throttle body, cleaning intake components, and checking for obvious leaks.
• Professional-priority or required cases:
  • Fuel rail pressure test and dynamic pressure checks (requires special tool).
  • Injector balance testing and possible injector replacement.
  • Fuel pump diagnosis or replacement.
  • EGR valve testing or replacement (some Civics have accessible EGR, but may require specialized tools).
  • ECU/PCM programming or reflash.
  • Thorough diagnosis when multiple substrings of fault codes co-exist or when emissions-related repairs are required.

Safety note: If working with the fuel system, comply with safety precautions and consider professional help if you are not comfortable handling high-pressure fuel components.

PREVENTION

• Use high-quality fueling and detergents:
  • Use reputable brands with detergents designed for direct-injection engines; avoid low-quality fuels or fuel with low detergent content.
• Maintain air intake health:
  • Regularly replace the air filter; inspect intake hoses for cracks or loose connections; ensure there are no leaks after the MAF.
• Regular sensor care:
  • Clean MAF sensor as needed (do not aggressively scrub); replace sensor if readings are erratic after cleaning.
• Maintain vacuum and PCV system:
  • Replace PCV valve and hoses per service intervals or if you notice surging idle.
• Maintain fuel system health:
  • Change the fuel filter (if applicable) according to the maintenance schedule; check for unusual fuel smell which may indicate leaks or injector issues.
• Drive cycle consistency:
  • Moderate trips that allow the engine to warm up fully help keep fuel trims stable; avoid excessive short trips that prevent the engine from reaching proper operating temperature.
• Emissions-aware driving:
  • Ensure catalytic converter health; abnormal exhaust or sensor readings can propagate fuel trim issues.

Final notes

• The P0172 condition is a fuel adjustment issue that could stem from sensors, fuel delivery, or intake/leakage problems. Because the 2022–2024 Honda Civic uses a direct-injection 1.5L turbo engine in many trims, carbon buildup and injector behavior can also influence fuel trim readings over time. Start with simple, non-invasive checks (air intake, MAF cleaning, vacuum hoses, O2 sensor condition), then progressively move to fuel delivery and sensor tests if the problem persists.
• In absence of official recalls or TSBs in the provided data, rely on standard diagnostic flow and Honda service manuals for exact diagnostic steps and specifications. If you’re attempting repairs beyond basic maintenance, consider professional service to avoid unintended harm or warranty concerns.
• If you’d like, I can tailor the diagnostic flow to your exact Civic variant (trim, engine code, and transmission) and provide a step-by-step checklist with real-world toggle points for your scan tool data.