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2 Corollas, 1 Tercel
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Discussion Starter #1
What are the possible long term ramifications of having a LEAN CONDITION BANK ONE? I have the P0171 code and will not have time to do a proper vacuum leak test for a couple of weeks. Car runs perfectly, no issues at all. Just wondering what might get damaged in the engine, if anything, if I drive it until I can locate the vacuum leak.
 

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1999 Corolla CE
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898 Posts
Oftentimes, a P0171 means that your Toyota is having trouble with a dirty or faulty mass air flow (MAF) sensor, or a vacuum leak downstream of the MAF sensor (perhaps in the PCV line or in the valve itself). Of course, this code can also signify a bad O2 sensor in bank 1.

Additionally, it's rare (but still possible) that a P0171 code can be tripped by a plugged fuel injector, by a dirty fuel filter causing low fuel pressure, or even an exhaust leak before the first O2 sensor€¦isn't engine trouble code diagnosis fun?

Most of the time, the best way to respond to a P017 is to try cleaning the MAF sensor and the lines running to and from it. This will often resolve this issue.
When you clean the MAF sensor, be sure to inspect all of the lines including the vacuum and PCV hoses. Look for kinks, cracks, etc. and replace the lines as needed. Additionally, be sure to check all of the connections and hoses on the air intake and check for intake manifold leaks.
Finally, it's never a bad idea to change your air and fuel filter, especially if they're just about due for replacement anyways.
If cleaning the MAF sensor and inspecting the lines doesn't solve the problem, it may be time to replace the O2 sensor on bank 1. Consult your Toyota's manual for its exact location, which is specific to model. If that doesn't do it, it's probably time to enlist the help of a professional.
 

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Senior TN Member
Porsche
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7,508 Posts
First test should be to measure intake-manifold vacuum as that will tell you 100% for sure if you do or do not have vacuum-leak after MAF. If so, continue with intake tract inspection. Sometimes, it's easiest to remove everything up to intake valves and re-install with all new seals and gaskets.

If manifold-vacuum is good, then skip intake testing and look at fuel. Measure pressure in fuel-rail. If not to spec, test filter, lines, FPR, pump. Measure injector flow and confirm volume and balance.

Measure O2 sensor with oscilloscope. No need to replace if it's working as designed.

 

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2 Corollas, 1 Tercel
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Discussion Starter #4
Thanks for your input guys. I've done the MAF things and visually checked the hoses, so I'm going to a professional.


My initial question was will the lean condition bank one damage the engine if I just leave it?
 
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