The Quick Answer above is the generic definition. What follows is what is documented for the Honda models that log P0172, checked against manufacturer data and owner reports.
DTC/P0172·Honda
P0172 on Honda: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Honda
P0172 on a Honda means the air-fuel mixture on Bank 1 (the cylinder bank with cylinder number 1) is running too rich: too much fuel for the available air. The ECU is already subtracting the most fuel it can, yet the mixture is still richer than the ideal 14.7:1 ratio, so it sets the code. The most common trigger is a dirty or over-reading MAF sensor that fools the ECU into adding extra fuel. Expect roughly 10 to 25 percent worse fuel economy until fixed.
Repair cost on Honda€8 - €350
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Honda Civic
2006-2024The 1.5L turbo in 2016+ Civics has a documented fuel-dilution issue where gasoline thins the engine oil; fuel-laden oil vapour re-entering the intake through the PCV system can richen the mixture and set P0172. Honda released a warm-up software update. Older R18A engines tend to see injector seal degradation at high mileage.
What causes P0172 on a Honda?
Beyond the generic causes listed on the main P0172 page, these are the documented Honda-specific patterns:
Honda CivicFuel dilution on the 1.5T enriching the intake via PCV vapour (2016+)
Honda CivicInjector seal degradation on R18A engines at high mileage
How to diagnose P0172 on a Honda with OBD2
Follow these steps to pinpoint the root cause of P0172:
- Check and replace the air filter if it is clogged or oil-soaked. This is the cheapest fix and rules out the simplest cause first
- Read live data with a scan tool: check short-term and long-term fuel trims (STFT and LTFT) at idle. Negative values beyond -8 percent confirm the ECU is pulling fuel out to fight a rich mixture
- Rev to 2,500 RPM and hold. If the trims return toward zero, the cause is idle-specific (a leaking injector or stuck purge valve). If they stay negative, suspect the MAF or high fuel pressure
- Inspect and clean the MAF sensor element with dedicated MAF cleaner, then re-test. A contaminated MAF is the most common single cause and cleaning is free
- Measure fuel pressure with a gauge at idle and under load, and compare to the manufacturer spec. Pressure above spec points to a failed regulator or restricted return line
- Check the coolant temperature sensor reading against the actual engine temperature, and scope the upstream O2 sensor to confirm it switches normally rather than reporting a false lean signal
- Inspect injectors for leak-down or dripping (a fuel-pressure leak-down test or a smell of raw fuel at the plugs) before condemning sensors
How much does P0172 cost to fix on a Honda? (EUR)
Estimated repair costs for P0172 in EUR, compiled across makes. Honda parts and labour usually land towards the lower end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0172 on Honda
These codes commonly cluster with P0172 on Honda vehicles:
Looking for the full P0172 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0172 guideSkanyx · Honda
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