What Does P0172 Mean on Your 2020 Honda Ridgeline?
The 2020 Honda Ridgeline is equipped with a 3.5L V6 engine producing 280 horsepower, paired with a 9-speed automatic transmission and available all-wheel drive. When your scanner shows P0172, the ECM has detected a rich fuel condition on Bank 1. On the Ridgeline's V6, Bank 1 is the rear bank of cylinders closest to the firewall, containing cylinders 1, 2, and 3.
A rich condition means the engine is receiving more fuel than the ideal 14.7:1 air-to-fuel ratio requires. The oxygen sensor detects excess unburned fuel in the exhaust, and when the ECM cannot compensate by reducing fuel delivery far enough, it sets this code.
Common Symptoms You Might Notice
- Check engine light illuminated
- Fuel economy worse than the expected 18/24 MPG
- Gas or sulfur smell from the exhaust
- Black soot on the tailpipe tips
- Rough idle or vibration
- Sluggish acceleration, especially when towing
Top Causes of P0172 on the 2020 Ridgeline
- Dirty MAF Sensor (35% likelihood): The Ridgeline's MAF sensor sits in the intake tube and is exposed to oil vapor from the PCV system and road debris. A contaminated sensor underreports airflow, causing the ECM to deliver excess fuel.
- Failing Bank 1 O2 Sensor (25% likelihood): The upstream oxygen sensor on the rear bank can degrade with age and mileage. A sluggish sensor delays fuel trim corrections.
- Leaking Fuel Injector (20% likelihood): A fuel injector on Bank 1 that does not seal completely will drip extra fuel into the combustion chamber.
- EVAP Purge Valve Stuck Open (20% likelihood): A stuck purge valve allows fuel vapors from the charcoal canister to continuously enter the intake, enriching the mixture.
How to Diagnose P0172 on Your 2020 Ridgeline
- Check for P0175 as well. If both banks show rich, the cause is shared (MAF sensor or fuel pressure). If only Bank 1, focus on bank-specific components.
- Inspect the air filter. The Ridgeline's air box is easily accessible. A clogged filter restricts airflow.
- Clean the MAF sensor. Remove and spray with MAF-specific cleaner. Let dry completely before reinstalling.
- Compare bank fuel trims. With a scan tool, check Bank 1 vs. Bank 2 LTFT values. If only Bank 1 is heavily negative, the cause is bank-specific.
- Test the purge valve. Disconnect the purge valve hose at idle and observe if idle quality changes.
Repair Options and Costs
- MAF sensor cleaning: $10 DIY or $60-$100 at a shop
- MAF sensor replacement: $150-$290 parts and labor
- O2 sensor replacement (Bank 1): $200-$400 parts and labor
- Fuel injector replacement: $220-$450 parts and labor
- EVAP purge valve replacement: $120-$270 parts and labor
Can You DIY This Repair?
The Ridgeline has a relatively accessible engine bay for a truck. MAF sensor cleaning and air filter replacement are easy jobs. The EVAP purge valve is moderately accessible. Bank 1 O2 sensor work is more challenging due to the rear-bank location, and fuel injector replacement on the rear bank requires significant disassembly. For those more complex jobs, consider a professional mechanic.
Prevention Tips
- Replace the air filter every 15,000-20,000 miles
- Clean the MAF sensor every 30,000 miles
- Use top-tier fuel to keep injectors clean
- If you tow frequently, consider more frequent fuel system maintenance
- Address check engine lights promptly to prevent catalytic converter damage