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GM expert tech
GM expert tech, ASE Certified Technician
Category: GM
Satisfied Customers: 152
Experience:  20+ yrs. experience, ASE Master Tech, GM STC trained
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what does lean bank 1 and lean bank 2 mean

Customer Question

what does lean bank 1 and lean bank 2 mean
Submitted: 7 years ago.
Category: GM
Expert:  Carhelp4u replied 7 years ago.
This means that both the right and left banks of the engine have been found to be running with an improper fuel air ratio. In this case you have more oxygen than you should causing for a lean condition. This problem can be caused by low fuel pressure, exhaust leaks, faulty injection components, or even vacuum leaks to the engine. Feel free to contact me with any questions or problems! Good luck!
Customer: replied 7 years ago.
i have checked for leaks and cant seem to find any can this also be caused by a bad o2 sensor and if so how do i know wich one i heard that there is 4 o2 sensors on my 1999 gmc yukon
Expert:  Carhelp4u replied 7 years ago.

I would not see a faulty oxygen sensor causing for a lean code on both banks. I really would recommend that you do a fuel pressure test to verify that this truck is getting 60-66 psi of fuel pressure.

Customer: replied 7 years ago.
i dont know if this can help but when i put my truck on the computer it gave me this code po171b bank 1 system too lean and po174b bank 2 system too lean
Expert:  GM expert tech replied 7 years ago.

Hi, I'm James. I have seen two problems that generally set these codes.

 

First, the Mass Air Flow sensor becomes contaminated and reports a lower air flow to PCM than actual, so PCM does not command enough fuel. You either need to clean MAF sensor or replace it.

 

Second, the intake manifold gaskets leak air so that the MAF sensor data again is too low causing a lean condition. GM has developed a new gasket to repair this problem.

GM expert tech, ASE Certified Technician
Category: GM
Satisfied Customers: 152
Experience: 20+ yrs. experience, ASE Master Tech, GM STC trained
GM expert tech and 3 other GM Specialists are ready to help you
Customer: replied 7 years ago.
Thanks james you were a great help.. i changed the mass airflow sensor and it seems to have fixed the problem... if i have any more questions i'll be sure to ask for your help as i'm in the process of trying to pass my emissions test..thanks again..
Expert:  GM expert tech replied 7 years ago.
You're welcome.