P0172System Too Rich Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- With closed-loop control the engine module corrects the injected fuel using the oxygen sensor: short-term fuel trim reacts within fractions of a second, long-term trim stores a learned base correction per load and speed range. Positive values mean fuel is being added because the mixture was lean, negative values mean fuel is being removed; around ±10 % is normal. P0172 means long-term trim on bank 1 is at its lower limit: the module already removes the maximum fuel and the mixture still stays rich. GM separates purge influence carefully: before the first purge it evaluates passively (factor 0.70 or below, i.e. −30 %), afterwards it closes the purge valve briefly for an active test, so a full charcoal canister is not counted as a fault. Ford only evaluates with purge off, at −25 %. Two trips. Bulletins name an open purge valve, leaking direct injectors and, on flex-fuel vehicles, a wrongly learned ethanol content. A permanently rich mixture can overheat the converter and dilutes the oil.
- What you may notice
- Check engine light on (after two drive cycles)
- Higher consumption, fuel smell
- Black smoke, sooted spark plugs
- Rough idle or starting problems after refuelling; converter damage possible later
- Likely causes
- LikelyPurge valve stuck open or charcoal canister saturated
- PossibleLeaking or dripping injectors (also direct injection)
- PossibleFuel pressure too high (faulty regulator, blocked return, regulator vacuum hose)
- PossibleFuel in the engine oil (short trips, leaking injectors), vapour via crankcase ventilation
- RareClogged air filter or intake, air flow sensor reading high; flex-fuel: wrongly learned ethanol content
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.