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Joined: Jul 2003
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In November I got the code p0171. Lean...Bank 1. I then replace the downstream O2 sensor (the upstream was repaced in July). So both O2's have been replaced yet the code is still coming up. I have replaced the fuel filter, and cleaned the connections to the O2 sensors. Car is not idling rough or stalling. Everything seems normal except for the gas milage. I have checked the archives but am still stumped on what to do. Help please?
Jason
98 Contour 4 cylinder z-tech ATX. 80000 miles
Mods: Tornado and K&N. (Both have been in there a couple of years before the problems).
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Joined: Sep 2002
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Hard-core CEG\'er
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You can try cleaning the MAF. It might do the trick. At least this procedure is cheap.
If a clean MAF doesn't get it, you will have to check for a vacuum leak in the intake tract.
Steve
98 Contour SE Sport 2.5 Duratec ATX The wifey's car
89 Taurus SHO - 246K miles
94 SHO ATX - 190K
1997 F-150 5.4L ATX - The Workhorse 150K.
ANY THREAD WITH "OMG" or "WTF" ETC IN THE TITLE WILL BE IGNORED!
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Joined: Jul 2003
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Newbie
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OP
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Joined: Sep 2003
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Yeah, have fun with this crap. My car has the same code to. Ironicly my mechanic says to replace the downstream O2 sensor. He says it is only reading "lean" and should be swutching back and forth, is that was yours said to? My upper O2 sensor was replaced in May.
Even more surprising my gas mileage has been low to since this code came about.
Looks like were in the same boat.
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Joined: Sep 2000
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CEG\'er
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CEG\'er
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Check for air getting in through ALL of the PCV connections. Even go as far as replacing the hoses and putting o-clamps around them to they're nice and tight. A P0174 will show up for similar reasons.
98.5 SVT now gone ... new wheels = 2005 330i
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Joined: Aug 2003
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CEG\'er
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CEG\'er
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Check for a vacuum leak also. One method is to listen for a leak. Another is to spray some carb or choke cleaner on suspect hoses and listen for the engine to stumble.
96 Sport 2.0L - 190,XXX miles
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Originally posted by HITMANinMI:
Yeah, have fun with this crap. My car has the same code to. Ironicly my mechanic says to replace the downstream O2 sensor. He says it is only reading "lean" and should be swutching back and forth, is that was yours said to? My upper O2 sensor was replaced in May.
Even more surprising my gas mileage has been low to since this code came about.
Looks like were in the same boat.
A downstream O2 sensor CANNOT cause a 0171 code.
You CANNOT get a 0174 on a Zetec.
Steve
98 Contour SE Sport 2.5 Duratec ATX The wifey's car
89 Taurus SHO - 246K miles
94 SHO ATX - 190K
1997 F-150 5.4L ATX - The Workhorse 150K.
ANY THREAD WITH "OMG" or "WTF" ETC IN THE TITLE WILL BE IGNORED!
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Joined: Jun 2000
Posts: 323
CEG'er
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CEG'er
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I have had this code on and off for years now. I have done everything mentioned above. Everytime I reset the computer and the CEL is gone for a while then i get the good ole' CEL. Then some time passes and the CEL gone, but it always seems to come back though  . Ive learned to live with it.  If you figure something else out, let me know. Good luck. Matt
'97 Pumice Zetec Sport- 'At least its not a geo!'
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"A downstream O2 sensor CANNOT cause a 0171 code."
Yes it can it did on mine.
He showed me the computer hooked up to it, the upstream was switching from "lean" to "rich" every second, the downstream was stuck on "lean". he said it should be switching because of the different fuel readings, he says no way should it be stuck on lean.
Who told you PO171 cant be the downstream O2?
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Joined: May 2000
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Hard-core CEG'er
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Hard-core CEG'er
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Originally posted by HITMANinMI:
"A downstream O2 sensor CANNOT cause a 0171 code."
Yes it can it did on mine.
He showed me the computer hooked up to it, the upstream was switching from "lean" to "rich" every second, the downstream was stuck on "lean". he said it should be switching because of the different fuel readings, he says no way should it be stuck on lean.
Who told you PO171 cant be the downstream O2?
Nope, you didn't listen, and I read your other post your mechanic both CLEANED the MAF (right) and replaced the downstream sensor (probably wrong)
Why?
Read here: http://www.findarticles.com/cf_dls/m0BQA/2_80/71847178/p3/article.jhtml?term=
Quote:
With the advent of OBD II, all vehicles utilize a heated sensor downstream of the oxidation catalyst to monitor cat efficiency Because a properly functioning catalyst will use up the excess oxygen in the process of converting HC and CO to CO2 and H2O, the oscillations in the rear O2 sensors should be minimal. Note that rear O2 sensors are not FLO. On the Ford models, the heaters on these rear O2 sensors are not turned on until the exhaust system has had a chance to toast out the moisture. This is done to reduce the chance of thermal cracking.
Notice bold part, which is what I told you before. Now if the engine was running lean, that sensor will stay lean, but that downstream sensor WILL NOT switch at the same rate as the upstream if the CAT is working properly.
In fact, if that downstream sensor begins to switch at the same rate, you will get a MIL for CAT efficiency as the PCM will think the CAT is no longer working.
So like I said about a week ago, you DON'T WANT the downstream sensor switching at the same rate as the upstream.
But hey, it's your money, so you can do the research and double check your tech, or you can just write a check, it's up to you.
TB
"Seems like our society is more interested in turning each successive generation into cookie-cutter wankers than anything else." -- Jato 8/24/2004
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