P0171, P0174 check engine codes - possible electrical problem?


Asked by Nov 30, 2012 at 09:35 AM about the 1999 Ford Windstar 3 Dr STD Passenger Van

Question type: Maintenance & Repair

I have a 1999 Ford Windstar 3.8L with the
check engine light on and reading codes
p0171 & p0174.

after a bachelors degree worth of research I
have taken many steps to troubleshoot and
fix the problem including: major tune up,
switch out the PCV valve, cleaned the Eger
valve, throttle body and idle air control,
replace the fuel filter, and inspected the
vacuum hoses.

I am aware that I can clean my mass air flow
sensor and possibly replace my oxygen
sensor, however, I have also noticed there is
a short in the electrical in various locations
in the vehicle.

the interior cabin lights come on randomly
when driving and I will need to adjust the
steering column or open the driver door and
shut it to turn the light off. there is also a
short with the seat belt light coming on even
when the seat belt is clicked.

I am beginning to wonder if the check
engine light can be coming on from an
electrical issue causing the o2 sensor or air
flow sensors connections to not get a proper

is this a possible for likely cause? any advice
and assistance would be appreciated.

28 Answers

For the P0171 and P0174 lean codes you need a high end scan tool to watch the fuel trim. The fuel trim is the correction the engine computer makes to the amount of fuel it allows to go into the engine to compensate for the readings it gets from the oxygen sensor. It's important to note what the readings are at idle and off idle and at WOT to determine when you have the lean problem. Knowing when the engine is running lean will point you in the direction to look for the trouble.

24 out of 24 people think this is helpful.

i.e. looks like a fuel/air fault not electrical. But what are the symptoms? What does the car do that's not right?

9 out of 9 people think this is helpful.

Those codes show up when un-metered air is detected. Look for a vaccum leak.

10 out of 10 people think this is helpful.

@David - SYMPTOMS: Periodically the car will sputter like it wants to die when idling in DRIVE or REVERSE; when I shift into neutral the sputtering stops/becomes very minor. I have been paying very close attention to this and have not noticed any particular pattern of when the sputtering occurs, it is completely random and not consistent. @Tom: I checked for vacuum leaks to the best of my knowledge (inspecting what hoses I know are vacuum hoses) however, that is about all I know to do. Are there any tips or tricks that you can share with me to know how to check for vacuum leaks?

33 out of 33 people think this is helpful.

1) Listen carefully. Yeah, I know over engine noise that is very difficult. 2) GENTLY pull on all vacuum hoses and see if one has no home, loose. 3) Look at not only hoses, but nipples that have nothing attached to them. When you put it in neutral there is no load and the leak will have less effect on engine, or none.

5 out of 5 people think this is helpful.

This is as big as I can make it, if you print it and enlarge you may be able to see vacuum routing

44 out of 44 people think this is helpful.

Thank you, should I pull them (vacuum hoses) with the vehicle running or with it turned off? Also, what am I listening for? Thank you for your time and assistance.

2 out of 2 people think this is helpful.

Pull on them with engine off, safer, (more safe?), and while it is running a hissing or sucking sound

2 out of 2 people think this is helpful.

Update: I have not checked for vacuum leaks yet as today was quite busy however, sometimes when starting the car, it will sputter and then stall out as if it is not receiving any fuel. I noticed today that when I start the vehicle and it begins to sputter, if I press the gas pedal and rev the engine to about 3000 rpms for a (not holding it there but just rev it and then let it go back down) that the car idles perfectly fine. I know that [engine misfire], [high fuel pressure], and [low-fuel pump or pressure regulator] can also set off these codes. Does the symptom that I just explained sound likely to be a fuel problem rather than a vacuum leak? This will help me to know where to start tomorrow and Monday when looking at it. I will keep you updated accordingly.

17 out of 17 people think this is helpful.

I am also having identical code 171 and 174 problems with a Ford 2003 Windstar with 60,000 miles. Check engine light comes on when idling at a long light in drive and possibly when driving slow in reverse. Engine has died several times at a long light. I bought the car six months ago and I suspect a dirty fuel filter. Fuel Filters are supposed to be replaced at 15,000 miles. (My interior dome lights also come on at odd times and go off when I open the drivers side door.) My mechanic sprayed fluid around the intake manifold, but no change in idle resulted. He cleared the codes and said to see what happened. I drove about 60 miles and the codes came back on at a long light.

30 out of 30 people think this is helpful.

I have a 2002 Windstar that had rough idle when the engine is cold initially. Then, the check engine light came on, with scanned code P0171 and P0174. I did the search on google and it appears to be Mass Air Flow (MAF)sensor issue. Before spending much money, I bought the Mas Air Flow clean spray by CRC. Disconnected the air filler tube, took out the plastic piece connected to the air intake, sprayed generously to clean the Mass Air Flow sensor without disassembling the sensor. Let it dry and put back. The idle is perfect and the car drives so much smoother now. According to someone who is the Ford mechanics that MAF sensor should be cleaned regularly 30K miles.

18 out of 18 people think this is helpful.

codes are P1150,code P1151 P1152,MIL, Monitrs,2INC, 02SNSR, 02HTR FUEL,COMP ,CATIYST,EGR,MISFIRE.


Well I replaced a few things in this order. And my problem is gone. The internet rocks you can find anything if you search hard enough. I replaced the crank position sensor first and the fuel pressure kept dropping. They must work together. I thought it was a fuel filter or pump. I changed the fuel filter too. I was driving and my 99 windstar would just cut out. I have a 3.8L V6 by the way. It would still run in limp mode but had a hard time starting sometimes too. No check engine light also. Then a week later my check engine light and Abs light came on. I went to Auto Zone and had them put it on a hand held scanner. Got a bank 1 and bank 2 lean codes. I changed the mas air flow sensor. Reset the codes by disconnecting the battery for 1 hr. Drove fine for a day. Then Check engine light again. So I was told to change upstream o2 sensors left and right. Then drove fine for a day. Then I changed pcv valve and rented a fuel pressure meter. I was holding 30 psi. it would taper off after i shut off the motor. thats okay i heard. Then i found a little tiny pin hole on the return fuel line on a bracket that rubbed a hole in the line. You will still keep fuel pressure cuz it is a return line. I patched it with some rubber fuel line and two hose clamps on each end. Never do this on a high pressure line. That is the one with the filter on it. I reset the codes once again by disconnecting the battery for an hour. Then i got that damn light again. Finally i gave the DPFE sensor or something like that. It controls the upstream and downstream in the computer. And now my problem is fixed.About $250.00 but way less than a garage or dealer who would just re program the computer and your van will just burn more gas. I replaced all the parts my self and I know its done right. Plus I got new parts all over my van and not just dignosis fees. I suck at spelling but i figured it out. Thanks to people like me posting things like this. Hope this helped.

20 out of 20 people think this is helpful.

Ford has issued a Technical Service Bulletin on this issue. Inspecting the Vacuum hoses may not be helpful as, from what I understand not being a mechanic, the leaking is actually located at the intake manifold gasket. The root cause is a bushing around the retaining bolts which causes air to leak. In order to fix and clear the codes, you need to replace the intake manifold gasket, replace the retaining bolts (all 8 of them). The new bolts have been redesigned to better handle the oily wet/hot environment.

12 out of 12 people think this is helpful.

I had the same issue with the interior lights coming on. I took the interior light dimmer switch apart and cleaned the contacts. It had been a year and no gremlins turning the interior on. I replaced my fuel pump 3 months ago because of starting issues. It fixed that problem. Now I am getting a stutter (acting like a misfire but no codes) when you start the engine after it was warm but sat for about 15 minutes. I tested the fuel pressure and it was good. It held pressure for 10 minutes after shutdown. I was relieving the pressure on the pressure line with the tester. I noticed that after the car sat for few minutes with key off that the pressure increased. I bled it a few more times. And pressure creeped up a little. I when I had the pressure drained, I removed the pressure regulator going yo the return line. Once it was removed, I noticed pressure on the return line and it kept spitting fuel from the return Does any one have ideas why there would be back pressure on the return line?

3 out of 3 people think this is helpful.

The newer Windstar also have a flapper valve that are internal to manifold and go through to the outside to the operation linkage which leak also, along with the none sealable bushing retension bolts makes it the worst intake design ever that I've seen in the 30yes working on cars. how this design ever got through any design review sure take my trust away from anything Ford makes!

2 out of 2 people think this is helpful.

i have a 2001 ford winstar xl it stutters like its going to die out when i start it and when i put it in gear or when im at a stop like it also iddle high for a few minutes everytime i start it im going 2 start with sencers but i reallly hate enything with a computer or fuel injected but i do all the work myself if u have eny ideals feel free to look me up on fb my name is gfhf ikilludead will be traveling with a carnival so will be on fb as i can hopen to get my van fixed and the stupid check ingene light 2 shut off

3 out of 3 people think this is helpful.

lordsmrfixit, i couldnt agree More! that flapper crap should have never been placed on ANY vehicle in the world.

2 out of 2 people think this is helpful.

This engine has a issue with the PVC valve sucking oil into the intake which degrades the O rings and gaskets. There is a after market kit at Auto zone to change out the forward valve cover and replace all of these seals. Depending on the length of time this has been going on you may have to change out one or more of the O2 sensors if they have become plugged. It is very common I fixed mine in about an hour.

3 out of 3 people think this is helpful.

It causes massive vacuum leaks.

1 out of 1 people think this is helpful.

its intake manifold that is leaking, just the upper, an easy fix

3 out of 3 people think this is helpful.

I have a 01 windstar sel it keeps blowing #9 fuse as soon as I turn the key on. And it's saying fuel computer data error. Van won't even turn over

4 out of 4 people think this is helpful.

Hi I had a question i have a pontaic g6 2006 and the engine light keeps coming on p0171 system ruining too lean bank 1. First I replaced the o2 sensor and mass air sensor and it came back on then I check for a vacuume leak and found none. Whenever the code on it has a hard time starting. I was wondering why it could be doing this

5 out of 5 people think this is helpful.

My vehicle my rpm is comeing up than 4 in pathfainder 2002

1 out of 1 people think this is helpful.

Your Answer:

So after all this jibber jabber above, does anyone know wtf causes the simultanious P0171/174 codes on the Windstar? Is it a vac leak, fuel issue, o2 sensor, MAF, PCV, intake gasket. Bueller, Bueller, Anyone, anyone?


Yes. There are 8 retaining bolts which do not hold up well under heat. Ford has redesigned these bolts for one better suited to the task. The reason your vehicle is throwing those 2 codes is that air leaks past the intake manifold gasket due to the faulty bolts. The 2 codes are simply the right and left cylinder banks. Replace the manifold gasket and the bolts and the problem goes away. It is noteworthy that according to a Ford Technical Service Bulletin that an additional step in the fix is to reflash the computer with new software to "make the sensor less sensitive to a lean condition". When air gets past the intake manifold gasket obviously the fuel mixture changes. Now the vehicle runs lean throwing the two simultaneous codes. I hope his helps.

3 out of 3 people think this is helpful.

Just to clarify, it's definitely not one of the other problems I listed, right? The reason I need to be sure is my wife works at a tech school and they always do what I tell them (mostly little stuff). If I get it wrong, they'll probably never let me tell them what to do again. I've never been wrong yet, but the intake gasket is more than they normally do, plus they hate working on this old clunker.

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