P0171 System too lean, bank 1
- System
- Powertrain - engine and transmission
What P0171 means
"System too lean, bank 1" is a statement about a correction, not about a part. The computer adds or subtracts fuel to keep the mixture where it wants it, and this code is filed when the correction it had to apply on bank 1 reached the far end of its range in the direction that adds fuel. Bank 1 is the group of cylinders the engine computer numbers first; P0174 is the same reading on bank 2.
This is a standard code. It means the same thing on every make of vehicle.
What the program shows for P0171
Short fuel trim and Long fuel trim are that correction, live on the Dashboard beside Air flow, Manifold pressure, Air/fuel ratio and whether Fuel system is in closed loop. Record a drive and the Analysis screen gives the total correction At idle, plots fuel trim against air flow, and says whether the air flow and pressure readings agree; recording again after a repair puts the two side by side.
The Dashboard shows Short fuel trim and Long fuel trim, Air flow, Manifold pressure, Intake air temp, Coolant temp, Throttle position, Accelerator pedal, Air/fuel ratio, O2 sensor (rear), O2 sensor current and whether the Fuel system is in closed loop. Record a drive and the Analysis screen gives the total correction At idle, Fuel trim against air flow, and whether the air flow and pressure sensors agree; the Full scan's On-board self-tests list the Oxygen sensor results by bank and sensor. Record before and after a repair and Compare shows the change in short, long and total trim at idle plus which codes are Gone, New or Still there.
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