A fuel mixture fault usually needs a check soon to avoid poor running and damage.
Trouble codes · P0172
P0172 meaning
System Too Rich Bank 1
The same first verdict Car Assist shows from this code alone, before a diagnosis. The code does not tell the app whether the warning light is flashing.
What this code doesn’t tell you
A code says where the car noticed a problem. It does not prove which part failed, whether the fault is still present, or what repair this car needs. The engine, other codes, freeze frame and live readings matter.
Usual causes, most likely first
The order is a starting point across cars; the exact engine and its readings can change it.
- Air flow sensor over-reading
- Leaking injector or excessive fuel delivery
- Purge valve stuck open
What you can check
With the engine off and cold, check the air filter housing is properly fitted and the intake is clear. Note hard starts after refuelling and changes in fuel use.
Words the car uses
- Stored codes
- Faults the car has confirmed and saved. They help explain a check-engine light, but a code alone does not prove which part needs replacing.
- Freeze frame
- A snapshot of the engine's readings when a fault was recorded. It helps show the conditions that caused the fault, even if the car now seems fine.
- Readiness monitors
- The car's own checks of its emissions systems. An unfinished check means the car has not tested that system yet, so a clean code scan may miss a fault.
- Fuel trims (STFT and LTFT)
- How much the engine computer adds to or takes away from its planned fuel amount. STFT is the immediate adjustment and LTFT is the learned adjustment; B1 and B2 identify groups of cylinders, and large adjustments can point to an air or fuel problem.
- Air and fuel balance
- How the engine balances air and fuel; lambda describes that balance. A requested value is the computer's target, rather than a measurement.
- Fuel vapour system (EVAP)
- The system that catches fuel vapour from the tank and feeds it into the engine. A leak can turn on the check-engine light, sometimes because the fuel cap is loose.
Find out what’s causing yours
Car Assist reads your car through an OBD-II adapter and your iPhone. Its assistant uses the codes, freeze frame and live readings to work through the likely cause with you.