CorollaFix

P0171 on Toyota Corolla E170: System Too Lean (Bank 1)

Short answer: P0171 means “System Too Lean (Bank 1)”. The car’s computer has found a fault in the Engine system and turns on the Check engine light (MIL). First check: read the code and freeze-frame data with an OBD-II scanner.

Standard OBD-II code Same meaning on all cars (SAE J2012). Not checked against this car’s factory manual.

Code
P0171
System
Engine
Dashboard light
Check engine light (MIL)
Applies to
Generic OBD-II meaning. Not every code is used by this car.
Confidence
medium (generic OBD-II definition, not checked against the factory manual for this car)
Source
obd-codes.com

Symptoms and when it is set

  1. Check engine light on
  2. You will more than likely not notice any drivability problems, although there
  3. May be symptoms such as
  4. A lack of power
  5. Detonation (spark knock)
  6. Rough idle

Likely causes

  1. A code
  2. P0171
  3. Has happened
  4. The MAF (Mass Air Flow) Sensor is dirty or faulty
  5. Air filters may cause the MAF to become dirty if the filter is over-oiled
  6. There is also an issue with some vehicles where the MAF sensors leak the silicone
  7. Potting material used to protect the circuitry

What to check, in order

  1. Read the code and freeze-frame data with an OBD-II scanner
  2. Check the connector and wiring of the part named in the code
  3. Test the part with scanner live data or a multimeter, using the values in the repair manual
  4. Fix the cause, clear the code and test-drive

Related on this car

Same code on other cars

← P0141 P0172 →

Clearing the code does not fix the fault. If it comes back, the problem is still there. For brakes, airbags and steering, see a trained mechanic.