trouble codes p171,p174

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Jan 18, 2011 | 05:42 PM

slapshot1989

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trouble codes p171,p174

I have a 99 explorer 4.0L. I am getting trouble codes p171 and p174. I have cleaned the MAF and changed the EGR valve already. I have done some research on this and am coming up with it's either the O2 sensors or there is an air intake leak (gasket). This started up a couple months ago and I have been working on it when I can. I don't really want to spend another $50 on an O2 sensor if it's the gasket. On the other hand, I don't want to take it in and pay $500 for a $50 sensor that I can put in myself. I'd like to know what others with this problem ended up getting fixed to take care of it. Thanks for your help.

Jan 18, 2011 | 06:58 PM

ncranchero

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From: E.Lincoln County, NC

You have a vacuum leak. Check closely the PCV valve and hoses. They are the usually the problem, more common than intake gaskets. It's not your O2 sensors. They both don't fail @ the same time.......

Jan 19, 2011 | 03:41 PM

MrSki

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Quote:

Originally Posted by ncranchero

You have a vacuum leak. Check closely the PCV valve and hoses. They are the usually the problem, more common than intake gaskets. It's not your O2 sensors. They both don't fail @ the same time.......

I'd agree but it's a big leak.

Jan 19, 2011 | 05:13 PM

fz1dave

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From: NW IN.

Since you've checked the MAF, and I'm assuming the vacuum lines, I'd have to say your problem is the intake gaskets (o-rings).

Those codes on my Windstar led to new intake o-rings and plenum bolts. A very common problem on the Windstars and not expensive if you can do the work yourself.

Jan 19, 2011 | 05:36 PM

ncranchero

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From: E.Lincoln County, NC

Quote:

Originally Posted by MrSki

I'd agree but it's a big leak.

Stuck open PCV valve or cracked line is big enough. The '01-up Sport Tracs have a real common cracked elbow problem that throws both of those codes together.

I do not think the OP's '99 has this same set-up though.

Feb 22, 2011 | 01:45 PM

Xscutout

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Have someone check for vacuum leaks with propane, it more accurate than the soappy way, I had also spent many dollars and time chasing codes.

Mar 4, 2011 | 07:44 PM

auxiliaryman

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Trouble Codes P171 and P174 (again)

I to own a 1999 Explorer (4.0 SOHC) with this issue of P171 and P174 OBD Codes and am seeking advice, have been troubleshooting for awhile, don't beleive I have a vacuum issue because manifold vacuum is a rock steady 18", I have 65 PSIG fuel pressure, replaced the MAF with no effect, funny thing is, the vehicle runs great, is not hard to start, just have these faults, anyone have any additional ideas...