P0171: System Too Lean (Bank 1)
Short answer: P0171 means “System Too Lean (Bank 1)”. It is a standard OBD-II code, so the basic meaning is the same on every car. Below is what it means on each of the 8 cars we cover, with a link to the full page for each car.
Standard OBD-II code Same meaning on all cars (SAE J2012).
P0171 on each car
| Car | Meaning on this car | Confidence |
|---|---|---|
| Toyota Passo (1st gen) | Fuel Trim System Too Lean (Air-Fuel Ratio Lean Malfunction, (P0171/25) | high |
| Toyota Vitz (1st gen) | Fuel mixture too lean (P0171/25) | medium |
| Toyota Corolla (9th gen, E120) | SYSTEM TOO LEAN(FUEL TRIM) (P0171/25) | high |
| Toyota Corolla (9th gen, E120) | SYSTEM TOO LEAN(FUEL TRIM) (P0171/25) | high |
| Toyota Corolla (11th gen, E170) | System Too Lean (Bank 1) | medium |
| Toyota Corolla (10th gen, E140) | System Too Lean (Bank 1) | medium |
| Honda City (5th gen, GM2) | System Too Lean (Bank 1) | medium |
| Honda Civic (10th gen, FC) | System Too Lean (Bank 1) | medium |
| Suzuki Wagon R (Pakistan, K10B) | System Too Lean (Bank 1) | medium |
Symptoms
- Check engine light on
- You will more than likely not notice any drivability problems, although there
- May be symptoms such as
- A lack of power
- Detonation (spark knock)
- Rough idle
Likely causes
- A code
- P0171
- Has happened
- The MAF (Mass Air Flow) Sensor is dirty or faulty
- Air filters may cause the MAF to become dirty if the filter is over-oiled
- There is also an issue with some vehicles where the MAF sensors leak the silicone
- Potting material used to protect the circuitry
What to check, in order
- Read the code and freeze-frame data with an OBD-II scanner
- Check the connector and wiring of the part named in the code
- Test the part with scanner live data or a multimeter, using the values in the repair manual
- Fix the cause, clear the code and test-drive
Causes and checks above are the general meaning. The exact test steps and values differ by car: open your car’s page.