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post #1 of (permalink) Old 05-25-09, 06:25 PM Thread Starter
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rainy day poco's Avatar
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system to lean bank 1

99 F150 V6 auto. Can anyone tell me what causes these codes
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0171 System Too Lean (Bank 1)
P0174 System Too Lean (Bank 2)
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post #2 of (permalink) Old 05-25-09, 10:56 PM
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Re: system to lean bank 1

P0171 and P0174 together usually indicate a vacuum leak.and that is most likely the cause of P0401 also.but P0401 could be egr valve,egr solenoid,dpfe sensor.gotta trouble shoot that one.but i would look for vacuum leaks first.
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post #3 of (permalink) Old 06-09-09, 11:30 AM
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Re: system to lean bank 1

i had the same code a while back, look under throttle body right in front, there will be a rubber elbow, about 3/4 inch in diam. that rubber elbow is replaceable, mine had a hole in it, if that isn't it, run your engine and feel around all the vaccum lines, mine also had a hole in a line coming from pcv valve to the back of throttle body, i just went to local auto parts store and bought some vaccum line and replaced it, it cleared all my codes and havent had any trouble since, thanks i hope this helps.

Last edited by kuntrybo; 06-09-09 at 11:31 AM. Reason: mispelled word
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