Question about Toyota Tacoma
Check engine light on, code reader says 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.
Posted on Sep 12, 2009
Vacuum leak, faulty O2 sensor, intake leak or injector stuck. You'll need to run a Volumetric efficiency calcutor or find someone who can, in order to determine the exact cause, combines with a scan tool observation at the same time.
Hope that helps.
Kevin, ASE certified
Posted on Sep 12, 2009
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Posted on Jan 02, 2017
It is a common problem, you will have to change bank 1, o2 sensor as it is covered in burnt oil and fuel telling the computer to run lean.
hope this help
Posted on Jan 17, 2009
SOURCE: Check engine light is on,
There could be a vacuum leak downstream of the Mass Air Flow sensor or the Mass Air Flow Sensor is dirty or faulty. Try cleaning the MAF sensor wire elements and clear the engine computer code. After removing the MAF sensor, spray the honeycomb inside the sensor, or the air meter with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling. Inspect all vacuum and PCV hoses, and replace any vacuum hoses that have cracks, cuts, etc. If it has been a long time since you changed your Fuel filter, it may be a good time to do this as well. This could also be due to a faulty O2 Sensor.
Posted on Apr 03, 2011
SOURCE: engine check light on error code
P0171 system too lean bank 1
P0174 system too lean bank 2
links to information on the codes
it means that the O2 sensors in your vehicle detected a lean condition in their respective banks. this could be caused by a dirty MAF (mass air flow) sensor or a vacuum leak downstream from the MAF sensor
sometimes you can clean the MAF with electronics cleaner or brake cleaner but be sure to take it off the vehicle first. be careful not to damage the MAF while spraying the cleaner, and allow it to dry completely before installing it on the vehicle.
Posted on May 21, 2011
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