Mixture: lean and rich
Lean and rich mixture. The best known codes grow from here — P0171 and P0172 — while the P21xx codes state the operating mode and the bank: lean only at idle means an air leak, lean only off idle means delivery.
11 codes in this section, 11 with a guide
What it usually turns out to be
- A lean mixture almost always starts with an air leak, not with injectors or the pump.
- Codes on both banks at once mean a shared cause: intake, fuel pressure or exhaust.
- Compare the fuel trims at idle and at 2500 rpm: the difference says where to look.
P0171System too lean (bank 1) — air leak or not enough fuelguideP0172System too rich (bank 1)guideP0174System too lean (bank 2)guideP0175System too rich (bank 2)guideP2177System too lean off idle (bank 1)guideP2178System too rich off idle (bank 1)guideP2179System too lean off idle (bank 2)guideP2180System too rich off idle (bank 2)guideP2187System too lean at idle (bank 1)guideP2188System too rich at idle (bank 1)guideP2189System too lean at idle (bank 2)guide
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Other sections
Fuel and air metering, general 33Intake measuring sensors 17Oxygen sensors 19Throttle and accelerator pedal 15Fuel and air metering: injectors 25Ignition system and misfires 29Exhaust gas recirculation (EGR) 7Secondary air injection 3Catalytic converter 4Canister and purge valves 9Fuel vapour leaks 7Fuel level in the tank 4Diesel particulate filter 6Idle and auxiliary systems 22Control module and its circuits 21Transmission 17Communication between modules 20Brakes, ABS and stability control 17Body, airbags and lighting 12