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Old 01-22-2011, 05:20 PM #1
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P0171 Code - Lean Bank 1... Help?

Hey Guys. I searched around, but couldn't find exactly what I'm having trouble with.

I have a recurring CEL popping up for P0171 - Fuel Trim System Lean - Bank 1.
When I hook up my bluetooth OBDII scanner, I notice the following:

O2 sensor 1 - acts normal
02 sensor 2 - acts normal
MAF - acts normal
Fuel trim bank 1, sensor 1 - Normal
Fuel trim bank 1, sensor 2 - ALWAYS READS 99.2%

The CEL light stays off until I am under heavy load (going up a steep hill)

Any idea what could be causing the constant high reading on Fuel Trim sensor 2?
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Last edited by jpontius; 01-22-2011 at 05:27 PM.
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Old 01-23-2011, 10:58 AM #2
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Last time I saw that code it was a broken hose from the PCV valve back to the throttle body. Vacuum leaks will cause that code.
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Old 01-23-2011, 09:48 PM #3
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but I don't understand why the fuel trim 2 would read 99.2% when the O2 sensors are reading normally. anybody?
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Old 01-24-2011, 10:42 AM #4
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I think I may have figured out part of my problem...

My downstream O2 sensor (bank 1 sensor 2, right?) is oscillating between .07 and .9 volts. From what I've read, this indicates that my catalytic converter is bad. Does that sound correct? If so, I'm still a little bit confused, because it seems to me that if the catalytic converter isn't working, the rear O2 sensor would see unburned fuel, indicating a RICH mixture. But in my case, it is detecting a LEAN mixture, and attempting to richen it with the fuel trim. Can somebody please help me try to make sense of this?

Other info:
First O2 sensor (Bank 1, sensor 1) oscillates between 0 and .9 volts, which I believe is normal.
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Old 02-17-2013, 09:54 AM #5
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Quote:
Originally Posted by FoneRunner View Post
Last time I saw that code it was a broken hose from the PCV valve back to the throttle body. Vacuum leaks will cause that code.
I assume that ALL of the vacuum hoses can be seen on TOP of the engine? (I'm an old 70's Ford guy am an use to one vacuum hose to the PCV valve to carb and maybe one more ....... no use to the spider web of black hoses under the hood.
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Old 02-23-2013, 11:00 AM #6
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Quote:
Originally Posted by CitadelBlue View Post
I assume that ALL of the vacuum hoses can be seen on TOP of the engine? (I'm an old 70's Ford guy am an use to one vacuum hose to the PCV valve to carb and maybe one more ....... no use to the spider web of black hoses under the hood.
After cleaning the MAF with the store bought spray and then a second time with alcohol ... I purchased a new Denso 197-6020 Mass Air Flow Sensor
and installed a new air filter .. I cleared the CEL and after 50 miles of driving no CEL ..... hope this was the fix .....
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