What Does P0172 Mean on Your 2021 Honda Pilot?
The 2021 Honda Pilot is powered by a 3.5L V6 engine producing 280 horsepower. This engine uses a V-configuration, meaning it has two banks of cylinders. Bank 1 is the bank containing cylinder number 1, which on Honda's J-series V6 is the rear bank closest to the firewall. P0172 means the ECM has detected that Bank 1 is running too rich, with excess fuel in the combustion mixture.
If you also see P0175 (System Too Rich Bank 2), both banks are affected, which usually points to a common component like the MAF sensor or fuel pressure regulator. If only P0172 is present, the issue may be bank-specific, like a single O2 sensor or leaking injector.
Common Symptoms You Might Notice
- Check engine light on
- Lower fuel economy than the expected 20/27 MPG
- Strong fuel or sulfur smell from the exhaust
- Black soot on the exhaust tips
- Rough idle or vibration at stops
- Sluggish acceleration
Top Causes of P0172 on the 2021 Pilot
- Dirty MAF Sensor (35% likelihood): The 3.5L V6 in the Pilot uses a single MAF sensor that measures all incoming air. If contaminated, it affects fuel calculations for both banks, but Bank 1 may trip first due to sensor positioning.
- Bank 1 Upstream O2 Sensor Failure (25% likelihood): The rear-bank O2 sensor can fail or become sluggish, causing the ECM to over-fuel Bank 1 specifically.
- Leaking Fuel Injector on Bank 1 (20% likelihood): A single leaking injector on the rear bank can cause enough excess fuel to trigger P0172 without affecting Bank 2.
- EVAP Purge Valve Issue (20% likelihood): A stuck-open purge valve introduces fuel vapors into the intake, affecting both banks but potentially triggering Bank 1 first.
How to Diagnose P0172 on Your 2021 Pilot
- Check for Bank 2 code also. If P0175 is present too, focus on common components like the MAF sensor. If only P0172, focus on Bank 1-specific parts.
- Clean the MAF sensor. This is the most common fix regardless. Remove, clean with MAF-specific spray, and let dry.
- Compare fuel trims between banks. With a scan tool, look at Bank 1 and Bank 2 STFT and LTFT. If both are equally negative, the cause is shared. If only Bank 1 is negative, the issue is bank-specific.
- Check the air filter. The Pilot's air box is easily accessible. Replace if dirty.
- Inspect the Bank 1 O2 sensor data. Watch the voltage pattern. It should oscillate between 0.1V and 0.9V at a regular rate. Compare to Bank 2 for reference.
Repair Options and Costs
- MAF sensor cleaning: $10 DIY or $60-$100 at a shop
- MAF sensor replacement: $140-$280 parts and labor
- O2 sensor replacement (Bank 1): $180-$380 parts and labor (rear bank is harder to access)
- Fuel injector replacement (single): $200-$400 parts and labor
- EVAP purge valve replacement: $120-$260 parts and labor
Can You DIY This Repair?
MAF sensor cleaning and air filter replacement are easy DIY jobs on the 2021 Pilot. The O2 sensor on Bank 1 (rear bank) is harder to access on the V6 because it sits between the engine and the firewall. This job often requires a flex-head O2 sensor socket and some patience. Fuel injector work on the rear bank requires removing the intake manifold, which is a significant job best left to professionals.
Prevention Tips
- Replace the air filter every 15,000-20,000 miles
- Clean the MAF sensor every 30,000 miles as part of routine maintenance
- Use top-tier gasoline to minimize injector deposits
- Have the fuel system serviced (injector cleaning) every 60,000 miles
- Do not ignore check engine lights, as catalytic converter damage is very expensive on a V6 with multiple converters