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CEL 0171 with AC on
#61247 05/20/02 12:09 PM
Joined: May 2002
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hugues Offline OP
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hugues
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Hi all:

Mercury mystique 96 std 2.0L

My CEL comes on (steady) with code 0171 (lean bank 1) when my AC is on (after 5-10 mns). If I reset CPU and do not use AC, the CEL stays off until next time I put AC on.

Any ideas ??

Hugues -
Re: CEL 0171 with AC on
#61248 05/20/02 10:53 PM
Joined: Dec 2001
Posts: 237
Alexandria, VA
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G Pappas Offline
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The following is from the Ford Technical Service Publication for your car:

Quote:
Diagnostic Trouble Codes (DTCs) P0171 bank (1) (cylinder #1) and DTC P0174 bank (2) indicate the fuel/air ratio is too lean. The fuel adaptive system is at the rich correction limit.

DTC P0172 bank (1) and DTC P0175 bank (2) indicate the fuel/air ratio is too rich. The fuel adaptive syste is at the lean correction limit.

DTCs HO2S Reference list:

-- HO2S-11 = DTCs P0171 and P0172
-- HO2S-21 = DTCs P0174 and P0175

Possible causes:

Fuel system
-- Excessive fuel pressure.
-- Leaking fuel injector(s).
-- Leaking fuel pressure regulator.
-- Low fuel pressure.
-- Contaminated injector(s)

Induction system
-- Air leaks after the MAF.
-- Vacuum leaks.
-- Restricted air inlet.
-- PCV system.
-- Fuel purge system.
-- Improperly seated dip stick.

EGR
-- leaking gasket.
-- Stuck open EGR valve.
-- Leaking diaphragm.

Base engine
-- Oil overfill.
-- Cam timing.
-- Cylinder compression.
-- Exhaust leaks before or near the HO2S's.

* Check air intake for leaks, obstructions and damage.

* Check air filter, air filter housing for blockage.

* Verify integrity of the PCV system.

* Check for vacuum leaks.

1996 Contour SE Sedan 4D (Royal Blue)
Duratec V6 2.5L 24-valve DOHC
Automatic
75,000 miles
No Mods (unless you call the DMD a mod)
Replaced EGR valve (gunked up), EVR (EGR VR), PCV valve, and evaporative emissions hose (cracked).
Re: CEL 0171 with AC on
#61249 05/20/02 11:52 PM
Joined: Jun 2001
Posts: 3,419
Conshohocken, PA
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PA 3L SVT Offline
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If it only happens when the AC is on, there might be another trickier problem hiding in there.

When the PCM determines that the AC is on, I believe that it adds to the calculated load value used in the fuel lookup tables (and even uses a whole different table possibly). IF this sensor is not properly reporting that the AC is on, this would cause the PCM to use the wrong part of the lookup table (and/or the wrong table). IF the AC being on requires more fuel than the lookup reports, the PCM will eventually give that extra fuel by looking at the O2 sensors and adding to the Long Term Fuel Trim. When the LT Fuel Trim gets too high, the lean code is thrown (LT plus Short Term greater than 30% throws P0171).

So, if you buy this idea, you need to check the sensor or switch that reports the AC being on to the PCM. Anyone with a good OBD-II scanner should be able to check that for you.

1998 Silver Frost SVT Contour born on...8/28/01[/i]
American Iron Shootout Radial Tire 2 Class Champion, Cecil County Dragway April 20, 2002
Re: CEL 0171 with AC on
#61250 05/21/02 11:32 AM
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hugues Offline OP
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Ok, thanks a bunch for the info. I appreciate.

I will look into the AC sensor thing since it throws the CEL only when AC is on.

Hugues -
Re: CEL 0171 with AC on
#61251 05/24/02 07:02 PM
Joined: Mar 2002
Posts: 31
Boston Ma
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SheiT Offline
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Whats goin on. Finally got to check my CEL light and got the same code P0171. I am the one also haveing the problem posted here-->http://www.contour.org/forums/ultimatebb.php?ubb=get_topic;f=3;t=007314.

Could this have to do with the same problem or most likely diffrent?

☼ §heiT
Re: CEL 0171 with AC on
#61252 05/24/02 07:41 PM
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hugues Offline OP
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Hi Sheit:

My CEL only comes with AC on. If I don't use AC,
it's okie dokie. I do experience some surging at idle some times (from 900 to 1100 rpm), which I don't think is a big deal (usually those come from vacuum leaks but it could be a lot of things).

If I were you,
I would reset the CPU to clear the code. You can just pull fuse 11 (I think that's the 1) for a few seconds and put it back. Drive without AC on for a few days (if you can manage of course). If no CEL, then start using AC. If CEL comes in, then we probably have same pb.

If CEL came back without AC on, I think others have experienced this so you can search forum for 'CEL 0171' and you shall find lots of info. Actually, a previous post on this very thread had the list of things to check with this code.

Hope this helps,
Hugues -
Re: CEL 0171 with AC on
#61253 05/24/02 08:00 PM
Joined: Jun 2000
Posts: 339
Connecticut
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MB Offline
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Connecticut
Wow i just got my CEL checked and same thing 0171 cylinder 1 to rich...but it doesnt happen with ac on though

Could this also be because of aggressive driving or lead foot syndrome?

So i could just pull fuse 11 to reset computer?

Matt

'97 Pumice Zetec Sport- Superchip/Apexi DTM Tip/KKM/blue lights/removed door dings/De-Badged/ford racing 9mm-blue/Custom Interior/indiglo gauges
Audio
-3 JL Audio 10s/-2 kenwoods amps/-JVC cd head unit (with 12 disc changer)/-6x8 pioneers
http://www.geocities.com/mattbchillin

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