Code 171 bank one too lean what is the cause - 2007 Toyota Corolla

Paul Thoegersen

• 95 Answers
• Posted on Jan 08, 2009

SOURCE: my code reader is showing a code of 171 O2 sensor bank one

Po171 is a lean condition on bank one ( only one) o2 sensor in front of the catalytic converter. Could be a mass air also could be a vacuum leak. or a bad o2 so dont jump to expersive parts unless you have another car to swap stuff around

SOURCE: bank 1 too lean

ALL CARS fixes are guessing and hoping at best. 1st thing is it a 4 cylinder or a v6. if its a v6 and you have bank 1 lean but NOT bank 2 lean, then you are probably looking for a vacuum leak affecting only bank 1. Stuck injector will NOT ause this code without also setting a misfire code. Cars use fuel trim. Basically you have BASE FUEL which is the preprogrammed best fuel amount for each condition. FUEL TRIM is the result of when the o2 sensor analyzes how rich or lean the car was, then adjusts the fuel trim to compensate as needed. Most cars set a trouble code around +/-25% fuel trim. You really need look at datastream on a scantool and determine if BANK 2 is also lean and just not quite at code level (IE - Bank 1 is at 25% and set a code, Bank 2 is at 22% and did not). In this case, tream it as a problem that affects ALL CYLINDERS instead of a bank.
Now that the bank thing is settled, lets presume you have a 4 cylinder. As said before, vacuum leaks are a common cause and should be checked early on. There are many ways to do this, but the cheapest and easiest is open the hood and listen for the air whistling/sucking sound and follow it. Doesnt always work, but you may get lucky.

SOURCE: obd 171 - too lean. what does this mean and how

If the vehicle runs out of fuel, the air-fuel ratio is Lean and DCT P0171 is recorded. the MIL then comes on. Try clear the P0171, see it come back on.

SOURCE: 05 corolla, after gassing up,

Sounds like you may have an issue with the check valve on your in tank fuel pump. When these go bad, you have to crank several time to build up enough pressure in the fuel rail for engine start. With a good check valve, the fuel pressure will not bleed off and the pressure is retained for the next engine start.