still getting PO171 - CEG Archives

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Hello,

I have been having this problem for month now autozone did free scan came up po171 they told me check oxygen sensors plus book says this. I replaced both upstream and downstream with correct ones and cleaned maf sensor and when reconnect battery stays off for like day. I took it back check codes again still same he said i had to clear codes from memory and he did this with scanner everything fine 2 days later light on again. grrrrrrr first trans had be rebuilt now 2 days after that been dealing with this cel.. Seems be running better after changed o2 sensors however still getting cel any other thoughts?? 98 ford contour se 4cyl

P0171 codes are normally NOT an O2 sensor issue. AutoZone strikes yet again!

Most likely, you have a vacuum/intake manifold leak.

Steve

I also checked haynes manual says oxygen sensor. Only after reading through this forum have I ever heard anything about Maf sensor and cleaning it so i tried that. Been looking on here and maybe I need new one wonder if could try one from junk yard? I mean if was 100% sure it is it I would fork out the money and get new 1 but right now I dont know. Wouldnt i hear vacum leak?

First off I had this code for a long time kept coming back to. Did everything replaced both O2 sensors, vacuum lines, cleaned, then repalced MAF, finally replaced injector O ring seals they leaked air on the intake stroke so it threw off the A/F ratio, and the code has been gone since October 2004 by the way.

thanks ill try searching for info on the injector O rings

Here

I wrote the How-To after I had to do mine

Originally posted by james05:
I also checked haynes manual says oxygen sensor.

Haynes....BAH! Better than nothing, I suppose....if you're out of Charmin...

Here is the list of possible causes for DTC P0171, P0172, P0174, and P0175 from the Service CD. Maybe it's just me, but I don't see any mention of an O2 sensor fault as a possible cause.

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H41 DTCs P0172, P0171, P0174 AND P0175: FUEL SYSTEM AT THE CORRECTED FUEL TRIM

Diagnostic Trouble Codes (DTCs) P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim 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 trim system 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 or running out of fuel.

-- Contaminated fuel injector(s).

-- Vapor management valve (VMV) leaking.

Induction system

-- Air leaks after the MAF.

-- Vacuum leaks (vacuum lines and gaskets).

-- Restricted air inlet.

-- PCV system.

-- Fuel purge system.

-- Improperly seated engine oil dipstick.

EGR System

-- leaking gasket.

-- Stuck open EGR valve.

-- Leaking diaphragm.

Base engine

-- Oil overfill.

-- Cam timing.

-- Cylinder compression.

-- Exhaust leaks before or near the HO2S(s).

l Check intake air system for leaks, obstructions and damage.

l Check air cleaner element, air cleaner housing for blockage.

l Verify integrity of the PCV system.

l Check for vacuum leaks.

l Are any of the above concerns present?

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Steve

Originally posted by projectSHO89:

Originally posted by james05:
I also checked haynes manual says oxygen sensor.

Haynes....BAH! Better than nothing, I suppose....if you're out of Charmin...

Funny but true! I have to use that in my sig!

hey thanks for all suggestion one standed out

Improperly seated engine oil dipstick.
don't know how but handle broke off my dipstick just recentely I tried pull it out using long nosed pliers got pushed in more bought a special magnetic tool from sears didnt work etheir my step dad said I can just drop oil pan and will come out so ill do that this week and try replacing seals om injectors fuel filter was just replaced month half ago before trans and we checked for vacum leaks today nothing thanks all for the tips glad weather getting nicer can try work on it some more this week. Pep boys claims they can pinpoint the problems from cel lights but they probality just say what book says so thats last resort..

Originally posted by james05:
hey thanks for all suggestion one standed out

Improperly seated engine oil dipstick.
don't know how but handle broke off my dipstick just recentely I tried pull it out using long nosed pliers got pushed in more bought a special magnetic tool from sears didnt work etheir my step dad said I can just drop oil pan and will come out so ill do that this week and try replacing seals om injectors fuel filter was just replaced month half ago before trans and we checked for vacum leaks today nothing thanks all for the tips glad weather getting nicer can try work on it some more this week. Pep boys claims they can pinpoint the problems from cel lights but they probality just say what book says so thats last resort..

I've got three suggestions for you.

First, you can possibly just unplug the dipstick tube & get the dipstick out that way. Could save you lots of time & potential leaks if you disturb the oil pan gasket.

Second, if you have checked your vac lines for leaks, sprayed about with Throttle Body cleaner to try & find leaks at the intake & TB, changed your air filter, checked the rigid PCV tube that comes from the front of the engine under the exhaust manifold and around the driver side of the engine, and cleaned your MAF, then your problem may be elsewhere. Do those checks first as they cost next to nothing & may solve your problem.

Third, try unplugging the MAF for a few days to see if the CEL goes away.

I have had a P0171 in my daughters Zetec for months now. The car has been so lean at low rpm that the valves have been chattering. Makes me sad & embarassed to drive it. Yesterday I took it to work for a change & was paying particular attention to the symptoms. Came to an intersection to make a RH turn, traffic was heavy so I had to hit the gas pretty hard to merge. As my foot began its plunge into the throttle, I cringed in anticipation of the horrid abuse the engine was about to take. Then, nearly no rattle as the car lurched through the turn, just a slight chatter at tip in, then it revved up pretty nicely. Checked that a few more times on the way home.

I got home, had dinner, and after the car cooled, I unplugged the Throttle Position Sensor (TPS). This morning I got in the car for my 20 mile commute & the car has run very well with no valve noise, no CEL code. The shifting has been off because of the unpluged TPS & I'm running off the fuel mapping tables in the ECU, but the car was running nicely overall. Today at lunch I'm going to plug the TPS back in to see what difference that makes - just to be sure I didn't disturb something else that fixed the problem. I'm gonna have the TPS checked & replaced if it's got a dead zone in it. I'll update later today...

Originally posted by TourDeForce:
I'm gonna have the TPS checked & replaced if it's got a dead zone in it. I'll update later today...

No joy.

This lean condition is driving me out of my mind! Eventually, I'll rip then engine bay appart & replace every freaking hose & seal that I can find...