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2.3L ('02-'11) 2009 Ford Ranger 2.3L p0171 code

bebyb

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2009
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Ranger XLT
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Automatic
Hello everyone, I have a "too lean" code on my 2009 2.3L Ranger. I am sure it has been covered many times before, but I figured I would post because everyone's situation is a little bit different. When it first came on it was on for a few weeks, then went away for a couple of days. Then it came back and has not gone off since. I have cleaned the MAF sensor and cleaned the throttle body. Since there is no other code like a MAF specific code or an O2 sensor code, I figured it wouldn't be likely to be either of those, or would it? My vacuum lines look good. Besides a possible vacuum leak, does anyone have any other ideas on what it could be? It has made my gas milage super bad.

Thanks!!
 


RonD

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If your MPG is bad then its a False Lean code, computer is running the engine richer than it should

A False Lean would usually indicated a failed Upstream O2 sensor or an exhaust manifold leak
O2 sensors "see" air/oxygen in the exhaust stream, not fuel
If there is an exhaust leak BEFORE the upstream O2 sensor then that SUCKS IN air while engine is running, causing a False Lean

And of course a failing O2 sensor can do the same, computer has no way to test upstream O2 sensors, and since its a 4cyl engine there is only 1 of these, so computer has to assume O2 data is OK, and as long as computer can added enough fuel to bring O2 sensor out of its lean voltage there would be no O2 sensor code, except for the False Lean condition

And it could be a computer issue

A vacuum leak or MAF sensor issue wouldn't effect MPG because the issue is unreported air or under reported air, so O2 detects too much air in exhaust and computer compensates for that and no drop in MPG

With a drop in MPG it means computer is actually running engine Richer than it should, so a False Lean
 
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bebyb

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Location
Nashville, Tennessee
Vehicle Year
2009
Make / Model
Ranger XLT
Transmission
Automatic
If your MPG is bad then its a False Lean code, computer is running the engine richer than it should

A False Lean would usually indicated a failed Upstream O2 sensor or an exhaust manifold leak
O2 sensors "see" air/oxygen in the exhaust stream, not fuel
If there is an exhaust leak BEFORE the upstream O2 sensor then that SUCKS IN air while engine is running, causing a False Lean

And of course a failing O2 sensor can do the same, computer has no way to test upstream O2 sensors, and since its a 4cyl engine there is only 1 of these, so computer has to assume O2 data is OK, and as long as computer can added enough fuel to bring O2 sensor out of its lean voltage there would be no O2 sensor code, except for the False Lean condition

And it could be a computer issue

A vacuum leak or MAF sensor issue wouldn't effect MPG because the issue is unreported air or under reported air, so O2 detects too much air in exhaust and computer compensates for that and no drop in MPG

With a drop in MPG it means computer is actually running engine Richer than it should, so a False Lean
Okay, I will try replacing that O2 sensor, thank you so much! One more question, my truck had the air bags deployed. Well, the air bags are fixed mechanically, but it has the air bag system light on and a regular scanner won't clear it. Do you know how to fix that issue?
 

RonD

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Have a friend put a Gloved hand over tail pipe while you listen in engine bay for an exhaust leak
If vehicle was in an accident then exhaust pipe could have cracked, engine and trans are heavy, so they don't stop instantly in a crash

On a 2009 you probably can't clear it
Were the seat belts/sensors replaced?
They also need to be replaced if they were being used when airbags deployed, they are considered unreliable after being used with that much force

Not sure on the 2009 but there are usually two modules involved, SRS for the airbags and RCM for the seatbelts
RCM is not reset-able has to be replaced as far as I remember
SRS can usually be reset but again not sure on the 2009??
SRS and RCM "talk" so both have to be OK or light stays on
 
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