Fuel & air mixture codes (P01xx)
The air-fuel mixture is too lean (too much air / too little fuel) or too rich (too much fuel).
Important: Content here is general information only, not professional mechanical advice or a diagnosis for a specific vehicle. When in doubt, have a qualified mechanic assess it promptly.
- P0171: System Too Lean (Bank 1) — Bank 1 of the engine is running lean — there is too much air, or too little fuel, in the air-fuel mixture compared with what the computer expects.
- P0174: System Too Lean (Bank 2) — Bank 2 of the engine is running lean — too much air, or too little fuel, in the mixture. It is the bank-2 twin of P0171, seen on V6/V8 engines.
- P0172: System Too Rich (Bank 1) — Bank 1 of the engine is running rich — there is too much fuel, or too little air, in the air-fuel mixture compared with what the computer expects. It is the mirror image of P0171.