P0171: System Too Lean (Bank 1)

P0171 means the air/fuel mixture is too lean — too much air or too little fuel — on the first bank of cylinders.

Symptoms

Rough idle, weak power, sometimes a ticking sound, higher fuel use or slight shaking, with a check engine light.

A vacuum/intake air leak is most likely, then a dirty MAF sensor, a clogged air filter, or low fuel pressure/injectors.

Check for air leaks first (cheapest), clean the MAF, and watch Fuel Trim via OBD2. Mowtar AI reads these values and ranks the cause.

Short-term yes, but a lean mixture can raise temperatures and harm the engine long-term — fix it soon.

Yes — P0174 is the same issue on Bank 2.