What component causes a p0171 system too lean bank one error code?
03-05-20, 09:38 PM
#31
Driver School Candidate
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Were you able to discover the problem? Im having same issues also. I have p0171 and p1150 code. I've already replaced A/F sensor on bank 2 sensor 1 with no changes. I took out my spark plugs 2,4,6, the new sensor, and they all had carbon build up. The new sensor was only in for 2 weeks. Cylinders 1,3,5 and and sensor bank 1 sensor 1 looked good. I can't find any air leaks either and cleaned maf sensor with maf cleaner.
03-07-20, 06:36 PM
#32
Pole Position
Were you able to discover the problem? Im having same issues also. I have p0171 and p1150 code. I've already replaced A/F sensor on bank 2 sensor 1 with no changes. I took out my spark plugs 2,4,6, the new sensor, and they all had carbon build up. The new sensor was only in for 2 weeks. Cylinders 1,3,5 and and sensor bank 1 sensor 1 looked good. I can't find any air leaks either and cleaned maf sensor with maf cleaner.
Your explanation seems kind of confusing. Just to be crystal clear - Bank 2 is towards the front of the vehicle, and contains cylinders 2, 4, 6. Bank 1 is towards the rear of the vehicle, and contains cylinders 1, 3, 5.
What sensor did you use? Is it OEM, Denso or aftermarket?
Did you try to disconnect the battery to reset the code? You can also try using a live data function on your OBD-II scanner to retrieve all the sensors' data.
Did you check all your vacuum lines? You can also try replacing the intake plenum gasket.
Also check your PCV valve and all the ventilation hoses.
How old are your air and fuel filters? Maybe those are already due.
It is generally not a good idea to try and clean Lexus MAF sensors, since those are what's called a Karman Vortex sensors. Read the directions on the cleaner. You may get away with it, but it is kind of a lottery, so be prepared..
Hope this helps and best of luck!
03-14-20, 01:38 PM
#33
Hello,
Your explanation seems kind of confusing. Just to be crystal clear - Bank 2 is towards the front of the vehicle, and contains cylinders 2, 4, 6. Bank 1 is towards the rear of the vehicle, and contains cylinders 1, 3, 5.
What sensor did you use? Is it OEM, Denso or aftermarket?
Did you try to disconnect the battery to reset the code? You can also try using a live data function on your OBD-II scanner to retrieve all the sensors' data.
Did you check all your vacuum lines? You can also try replacing the intake plenum gasket.
Also check your PCV valve and all the ventilation hoses.
How old are your air and fuel filters? Maybe those are already due.
It is generally not a good idea to try and clean Lexus MAF sensors, since those are what's called a Karman Vortex sensors. Read the directions on the cleaner. You may get away with it, but it is kind of a lottery, so be prepared..
Hope this helps and best of luck!
Your explanation seems kind of confusing. Just to be crystal clear - Bank 2 is towards the front of the vehicle, and contains cylinders 2, 4, 6. Bank 1 is towards the rear of the vehicle, and contains cylinders 1, 3, 5.
What sensor did you use? Is it OEM, Denso or aftermarket?
Did you try to disconnect the battery to reset the code? You can also try using a live data function on your OBD-II scanner to retrieve all the sensors' data.
Did you check all your vacuum lines? You can also try replacing the intake plenum gasket.
Also check your PCV valve and all the ventilation hoses.
How old are your air and fuel filters? Maybe those are already due.
It is generally not a good idea to try and clean Lexus MAF sensors, since those are what's called a Karman Vortex sensors. Read the directions on the cleaner. You may get away with it, but it is kind of a lottery, so be prepared..
Hope this helps and best of luck!
03-17-20, 04:06 PM
#34
Cpthaddock
What valve cover?
What expensive parts did I replace?
Car is 20 years old,
Random misfires and lean code.
I changed B1 upstream AF sensor with aftermarket for $25 (which was probably due anyway)
Cleaned MAf,as a test, FREE
Bought new one for $13 to test it (kept old one)
Front VVTI for front bank (2,4,6,) for $14 as a test (kept old one)
Replaced ECT coolant sensor $8
For a car that cost $30,000 when it was new this is not expensive maintenance, especially for things that wear past 100k miles anyway.
An easy test is to swap the B2 AF sensor which is good to the B1 Af sensor which is causing the code to see if that is the problem or not, if not then it is obvious a small leak between cylinder head/header and end of Y pipe
By the way we did a smoke test and still cannot find the leak because the space is very tight from the cylinder/header to the y pipe, especially when the engine has to be running and the fan is on pushing extra air around. End of Y pipe gasket and springs are good, cannot get up to B1 header gasket.
This is not my first rodeo, you make it sound like you can do for free in 5 min. My labor is free and the parts are not expensive, regular shop will charge you $60-100 for labor.
But anyway the transmission works in OD now and car runs fine, Code still there, I will swap Af sensors from B2 to B1 to see if code comes up, if it is then is obvious air leak not the new Af sensor I replaced in B1.
What valve cover?
What expensive parts did I replace?
Car is 20 years old,
Random misfires and lean code.
I changed B1 upstream AF sensor with aftermarket for $25 (which was probably due anyway)
Cleaned MAf,as a test, FREE
Bought new one for $13 to test it (kept old one)
Front VVTI for front bank (2,4,6,) for $14 as a test (kept old one)
Replaced ECT coolant sensor $8
For a car that cost $30,000 when it was new this is not expensive maintenance, especially for things that wear past 100k miles anyway.
An easy test is to swap the B2 AF sensor which is good to the B1 Af sensor which is causing the code to see if that is the problem or not, if not then it is obvious a small leak between cylinder head/header and end of Y pipe
By the way we did a smoke test and still cannot find the leak because the space is very tight from the cylinder/header to the y pipe, especially when the engine has to be running and the fan is on pushing extra air around. End of Y pipe gasket and springs are good, cannot get up to B1 header gasket.
This is not my first rodeo, you make it sound like you can do for free in 5 min. My labor is free and the parts are not expensive, regular shop will charge you $60-100 for labor.
But anyway the transmission works in OD now and car runs fine, Code still there, I will swap Af sensors from B2 to B1 to see if code comes up, if it is then is obvious air leak not the new Af sensor I replaced in B1.
Last edited by samsonn25; 03-17-20 at 04:13 PM.
03-17-20, 07:26 PM
#35
Driver School Candidate
even from rock auto I wouldn’t be able to match the prices you’re telling me, but good for you if these are quality parts.
I’d suggest getting a scan tool that has graphing capability. You’ll be able to much more easily see obvious problems with the AF sensor and you’ll be able to diagnose problems more easily in the future too.
a $25 upstream af sensor may not be a wideband af sensor, are you sure the one you bought said it was wideband? Or at least Canada/california spec? I know because I bought one for $30 just to try it out and it is simply not accurate enough and will still give you the code.
for me, when the OD fails it’s either a knock sensor or the heater of the at sensor failing.
Your best bet to find an exhaust leak is to put the car up on a lift and plug the muffler with a rag. You’ll see pretty quickly if and where there is a leak. Also, I don’t trust the CEL on this car. Just like the fake “coolant temp sensor” code.
Oh one more thing, can you test the fuel pressure? Lean codes are tripped when the computer detects the fuel trim is out of whack but on this car that’s only measured by duration of opening of the fuel injectors, not actual fuel amount delivered. The computer might be trying to inject more fuel but if the pressure is low then it will always be lean.
keep us updated. Thanks
I’d suggest getting a scan tool that has graphing capability. You’ll be able to much more easily see obvious problems with the AF sensor and you’ll be able to diagnose problems more easily in the future too.
a $25 upstream af sensor may not be a wideband af sensor, are you sure the one you bought said it was wideband? Or at least Canada/california spec? I know because I bought one for $30 just to try it out and it is simply not accurate enough and will still give you the code.
for me, when the OD fails it’s either a knock sensor or the heater of the at sensor failing.
Your best bet to find an exhaust leak is to put the car up on a lift and plug the muffler with a rag. You’ll see pretty quickly if and where there is a leak. Also, I don’t trust the CEL on this car. Just like the fake “coolant temp sensor” code.
Oh one more thing, can you test the fuel pressure? Lean codes are tripped when the computer detects the fuel trim is out of whack but on this car that’s only measured by duration of opening of the fuel injectors, not actual fuel amount delivered. The computer might be trying to inject more fuel but if the pressure is low then it will always be lean.
keep us updated. Thanks
Last edited by Cpthaddock; 03-17-20 at 07:30 PM.
03-04-22, 12:34 AM
#36
How fine exhaust leak
unfortunately, you have wasted a lot of money replacing parts which were most likely in perfect condition. The likely cause for a lean code in a 20 year old car is an exhaust leak before the A/F sensor (aka o2 sensor in the upstream, depending on the market where the car was sold). Ensure you have no leaks in your exhaust. Stop changing parts when you have done no diagnostics to them, at this point any mechanic who isn’t a complete joke could have solved this for you for much less than what you paid to replace half your cars electronics. I’d also ask for my money back from the scammers who sold you a valve cover??? It’s insulting what some garages will do. Good luck
03-05-22, 01:29 PM
#37
Examples of black soot and a smoke test on my exhaust before it was repaired/replaced.
I had an intermittent P0171 and an intermittent misfiring condition for random cylinders.
My issue was chewed wiring on the B1S1 A/F sensor. Replacing the damaged sensor resolved the issue.
Chewed sensor wires
Last edited by Hayk; 03-05-22 at 01:35 PM.
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