Codes: P0171  P0174  P0401
Check Engine Light

Get'n Rid of Them There 171 and 174 Codes on Your Windstar

... and how 'bout them P0401s too!

Additions will be preceded by a yellow asterisks.
Updated: September 20, 2009

Here is some information that may help you perform the recommended maintenance/repair to your Windstar when the Check Engine Light (CEL) comes on and codes 171 and 174 appear when retrieved from the computer.

* If you found this page through Google or some other search engine I think you will truly want to check out I found this site a great source of information regarding this and other auto-related subjects. People that post there have been very helpful as well. In my experience, this sites has not been like other forums, where those who ask questions are ridiculed, schoffed at, and told to RTFM! I think you will really like the site and will find it very helpful.

I found this a simple repair for me. I am not a mechanic by trade, but I have extensive experience with automotive maintenance, repairs, rebuilds, and restoration. This repair took me about 2.5 hours. You should have similar results I'd think.

First some legal stuff.

The information contained herein is presented with no expressed or implied warranty or promise with regards to any of its content. Further, if you use the contents shown herein as a guide you could break something if you have much, little or no experience with automotive mechanics. If you chose to continue, you do so at your own risk. I shall not be held liable for any damages caused by your interpretation of this document, references to it, your use of it, or anything you may do either on purpose or accidently to your any anyone's vehicle.

I am quite sure some pros will have various comments, corrections, slams, et cetera to say about what's to follow... that's all good. Information is great!

There is a Technical Service Bulletin that discusses the problems and suggested remedy. Many people have posts about this. The TSB I received helped to ID the parts needed for this repair, but lacked any usable information about how to perform the repair itself. The parts you will need are:

Part NumberQuantityWhat is it
1.XF2Z-9H486-AA1 pkg of 6Port Seals
2.3F2Z-9S479-AA1 pkg of 8, [Green-sleeved bolts]Isolator Bolts
3.XF2Z-9E498-DD1 ea.Vacuum Line, U-Shaped
4.*3F2Z-6582-BA1 ea.Valve Cover - LH
5.XF2Z-9461-AA1 ea.Upper intake halves seal

*Item 5 (above) is not part of the TSB, but can be replaced during this procedure. Also, as a user (rider54) at mentioned, you can change the right side spark plugs with the top half of the engine and cowling removed. Of course, that's if you get a hanker'n too...

*Check the U-Shaped vacuum line (Item 3 above) on your car before you buy a new one. Mine was like new... yours may be too. In retrospect I wouldn't have replaced mine. This vacuum line [Ringed in Red] is shown in the first picture below.

Now, many people suggest not replacing the valve cover. I chose to replace it as recommended. It was pricey... about $60.00 for it alone. It is up to you of course, but I recommend replacing it, if you believe you will keep the vehicle.

Take your time and get everything ready before you begin. Here is a list of the tools I used for this repair.

  1. Various small metric box and open end wrenches
  2. Various metric regular and deep sockets
  3. 1/4" ratchet wrench and 2" extension
  4. Channel-lock pliers
  5. Flat screwdriver
  6. Small pick (scratch awl)
  7. Flashlight
  8. Shop-Vac
  9. *Acetone
  10. *Mineral Spirits
  11. Rags


Now, let's get started.

Loosen and detach the negative cable on the battery. Sorry... no picture.

Valve Cover
Left (front-most) Valve Cover

Here's the first picture. Carefully remove the Positive Crankcase Ventilation (valve) [Yellow Dot] from the valve cover. Also disconnect the other end from the throttle body. Retain this. I had to clean it as it was very oily inside. I rinsed it (the valve and plastic pipe) with mineral spirits.

*I have been getting many direct e-mail with regards to these pictures and site. Thanks one and all. Many have been about the DPFE. The DPFE is shown in the [Green Box] in this updated photo. Soon after I did the TSB for the isolator bolts I started getting P0401 codes. Reading a little I learned that about 90% of the P0401 codes are caused by the DPFE. If yours is metallic like the one shown above, it is likely as crappy as mine and should be replaced. The newer model is made out of black polycarbonate or other similar material. I replaced mine three weeks ago (right before Christmas 04) and all has been well since. Cost just over $50 out the door. BTW: I drilled out the rivets on my old DPFE. It was terribly corroded inside - the enternals (differential sensor seals and circuit card) where shot. There are no replacable parts inside the DPFE so you will have to buy a new one if you suspect yours is defective.

Oil Seep Hole Inspection
Oil Seep Hole Inspection

After the PVC valve has been removed. Look down inside the hole at the five o'clock position. You will likely need to use a flashlight. You can just barely see the edge of the hole peeking out in this picture. If there is a 1/8" hole in there like the one shown in this "staged" photo. You should replace the valve cover. This hole is part of the culprit that lead to needing this repair. Please note that that new valve cover does not have the hole - I faked this image for demonstration purposes.

Dip Stick Problem
Loosen the Dip Stick Retainer

Notice the blue arrow. I removed the retaining bolt that holds the dip stick tube in place. Do not remove the dip stick tube, but you can remove the dip stick to get it out of the way if you'd like. Without doing so, I could not remove the spark plug harness clamp that is immediately behind the oil dip stick. Without removing the harness the valve cover bolt below the harness could not be loosened and removed.

Remove the left-bank spark plug wires that are just below the valve cover we will be removing. Give them a twist and then pull toward the front and driver's side of the van to get them off.

Remove all the bolts [Red Dots]. Most will not come all the way out but the one in the lower right corner of the image does. As a matter of fact, the new valve cover does not come with this bolt. You will need it when you put the new cover on - keep it handy for use later.

* I've been asked if the valve cover gasket is reusable. I can't remember if the new valve cover came with a new gasket or not. If anyone has the answer, please let me know. The intake's gasket was reusable though. It's likely the valve cover's could be as well.

Rubber Fresh Air Tube
Rubber Fresh Air Tube

I found it easier to work on this repair with the air cleaner out of the way. Loosen the two screws shown here [Red Lines]. Once, loose carefully remove the rubber tube.

MAF Sensor  Connector
MAF Sensor Connector

Now prepare to remove the Air Cleaner and *MAF sensor tube. Before you do this you will have to disconnect at least one connector. On my Windstar this connector was placed between the rubber tube (removed above) and the battery. I indicate it with the [Yellow Dot] here. Do not yank on this connector to disconnect it. There is a little tab to depress near the left side. Once depressed the connector separates easily. If yours isn't coming apart you may not have the tab depressed far enough. Once the connector is apart, pull the part that leads to the MAF from its mount. (Thanks for the information on the MAP vs. MAF sensor Serge!)

Air Cleaner
Air Cleaner

While the Air Cleaner and MAF Tube should come out as one unit it is easier to remove the halves of the air cleaner assembly separately. To do this, release the clasp [Red Dot] and separate the MAF from the Air Cleaner [Blue Dots]. The MAF tube is the one on the left. Air Cleaner is on the right. Check the filter. Replace it if necessary. Remove the Air Cleaner housing by carefully wiggling it back and forth while pulling straight up. Two rubber mounts as well as the snorkel hold it in place. You should find that it comes out easily.

Other Sensor Wires
Other Sensor Wires

In this picture two more connectors have been identified [Red Dots] to the left. These come apart easily too... if you press the little tab - normally on the male part of the connector. The [Red Dot] on the right is the MAF sensor connector discussed previously.

Throttle Control Cables
Throttle Control Cables

Next you will have to remove the throttle and cruise control cables. This is a cinch. First remove the bolts that hold them where they are supposed to be. The top bolt [Red Dot] is pretty easy to get to. The other one [Red Arrow] was a bit more difficult. Patience! After the bolts are removed detach the cables.

Throttle Cable Attachements
Throttle Cable Attachments

This picture was taken from behind the engine. Don't ask! Check this picture. The throttle cable with the plastic sleeve [Blue Dot] detaches by snapping it to the right in the picture, then it can be pulled out toward the firewall. The other one [Red Dot] can not be easily removed until the two bolts in the step above are removed. One of those bolts are shown here too at the [Yellow Dot]. The lower cable is attached around the throttle mechanism and in a slot. If you have ever messed around with a bicycle's hand brakes you will see a direct similarity with this fixture. It will come apart and go back together easily. Once you have the fasteners (bolts) removed, and the cables loose, position this part out of the way. {The throttle cable removal steps has been corrected... KDS input... thanks!.

Vacuum Lines
Vacuum Lines

Now let's get to the good parts. Here's another picture from the back side of the engine. This one is looking from the driver's side towards the passenger side. The camera was just to the left of the brake master cylinder. Here, I have pointed out several vacuum lines that will have to come loose. Heat had temporarily fused mine on! You will find it much easier to remove these lines if you push them on further first, then wiggle them loose. Each has been denoted with a [Red Dot]. Take note that the large vacuum line [Yellow Dot] is held in place with a clamp. Use pliers to loosen the clamp and move it back about two inches from the end of the hose. Remove only one end of the hose. They will not be a problem and will generally stay out of the way.

You may find it much easier to remove the vacuum lines from the plenum after the top half is removed. I didn't evening think to do this, but it's a great suggestion. Thanks KDS.

Intake Plenum
Intake Plenum

First, the little stuff. Disconnect the little vacuum line shown here [Yellow Dots]. Push the connectors on, then pull them off. This helps break them loose. Now... the TSB said replace this. Mine was fine. No oil contamination at all. I replaced it anyway since I had already purchased the part. But like I said above... check yours before you buy the new one. You may not need to replace it.

*I didn't remove the cowling when I did this work, but many people who have found this web document recommend it. In retrospect, I do too. (Thanks for the input Mapdog.)

*If you want to remove the cowling here's the procedure for doing this. Thanks again KDS. The cowling which prevents easy removal of the plenum lid contains the windshield wiper motor and linkage to the arm pivots. Be careful prying on this as it can damage the wiper linkage.

It was easy to remove this with the following steps:

Next, remove the 14 bolts [Red Lines] on the plenum. Keep track of which one goes where. This is important because they are different. These come out pretty easy; however, the ones furthest from you will take a bit more time for obvious reasons. Keep all these bolts. The plenum is in two parts. The top and bottom. Inside is a baffle (or air conduits that guides air down into the intake. Be careful with all these parts. You should not have to pry on any of them. Once I removed the 14 bolts, the top part of the plenum was loose without any force or pressure exerted. Problem was... I could not get it off the damn engine! The cowling [Blue Line] was about 1/2" too low, or the engine was 1/2" inch too high. In any event I had to get my son to carefully pry up on the cowling. I used a 2" wide piece of pine and only pried up enough to get the plenum off the engine. Note the sensor body near the [Green Arrows]. I use it as a fulcrum. Be careful not to pry against the shiny looking dome on it [Blue Dot]... pry to the left of that - on the body of the fixture. Again... do this carefully. I didn't have to exert much force at all during testing before handing this over to my 17-year old.

As suggested above, if doing this again, I'd remove the cowling to avoid prying on sensitve parts!

Intake Plenum Gasket
Intake Plenum Gasket

Once you remove the plenum you will find that there are two parts. One, the baffle which snaps into; two, the plenum. Clean these parts with mineral spirits. Mine where way grody inside. Also, check the [Red Line] in this picture. This represents the plenum gasket. It is one long gasket that goes all the way around the plenum. I carefully removed this and retained it. The recommended parts list from the TSB did not include this gasket so don't break it. When I put the engine back together I found that this gasket had magically grown. It was about 1/2" too long in its circumference. I kept messing with it until it got it to stay put.

Plenum w/ Top-half Removed
Plenum w/ Top-half Removed (Internal baffle not shown)

The culprets of the P0171 and 174 codes... bolts with black shoulders [Red Rings]. Evidently Ford saw fit to put parts in the engine that cannot take oil. The black-shouldered bolts are problematic it this regard. These are the Isolator Bolts. In any event, remove each one. They come out easily. There should be eight of them. Once they are out. Remove the lower part of the plenum chamber. Flip it over. You will find six small circular gaskets. Remove these and toss them in the trash. They will be replaced.

EGR Ports Exposed
EGR Ports Exposed

Peer down onto the top of the engine. You will see some gadgets that look like butterfly valves. Forget them. To the front of the engine you will see a hole that goes down. Don't drop anything in there. Keep looking around and you will see six nickel-size things that stick up towards you [Red Rings]. Each has a little hole in the center. On my car these (the holes) are about 1/8" in diameter. These are the Exhaust Gas Recirculation (EGR) metering holes. These should be cleaned. This is where the shop-vac and pick come in. Fire up the vacuum and while placing the nozzle near each of these little orifices clean them up. They weren't too bad on my Windstar.

Super Close-up of EGR Port
Super Close-up of EGR Port

This is really nice close-up of the EGR port. Notice the crud built up around the port's oriface [Red Arrow]. That stuff get's cleaned out.

* I didn't touch on clean-up of the parts too much in the first cut of this page. Here's some more information. Before you begin putting the top of the engine back together make sure you clean the intake manifold to intake plenum mating surfaces. This is the area where the six rubber gaskets go. I used a little acetone on these surfaces to cut through the built-up residue that was there. Using a razor with a very low angle of approach these surfaces cleaned up great. Be very careful with the razor. You will be working on aluminum and it scratches REALLY easy. Also, keep the vacuum near by and in use during this careful cleaning process. The vacuum sucks up debris before it has a chance to fall down into the intake ports.

Nicely Cleaned Intake Ports Faces
Nicely Cleaned Intake Ports Faces

When you are ready, begin reassembly. This is basically a reverse order of everything discussed herein.


Locate and install the six new intake gaskets. These go on the bottom of the intake plenum that came off last. Ensure the little tabs on each goes in the little slots. They will stay put without any sealants.

Now put on the vacuum lines on the back of the engine. Don't forget to move the clamp back into place. Also begin reattaching spark plug towers and wires.

Now carefully place the lower plenum half on the intake. Install the new Green-Shouldered Isolator bolts (8 ea). I would like to tell you the torque specs for these and other bolts, but I do not know it. I've heard that Haynes says 89 ft.lbs and others said it says 89 in.lbs. I don't have the book myself but I'd say it is in.lbs. If you don't have an inch pounds torque wrench use 7-11 ft.lbs. If you don't have a torque wrench at all, here what I did. It worked for me. I ensured mine were not overly tight, but nicely snug. How's that for being right on. You pros oughtta love that one. Keep in mind that you are clamping together aluminum and plastic. This thing isn't going into space so don't over-do it. I would tighten these from the center two and go towards the outside bolts in a cris-cross pattern. I tightened mine down in three steps using the same sequence each time.

*More from KDS. Great additional info... The isolator bolts have metal shanks in them that prevent compression and possible crack damage to the plenum. You can tighten them without breaking the plenum, but attempting to torque them to Haynes specs (89 ft-lbs) will likely cause them to snap off. KDS saw that the first bolt maintained about 20-30 ft-lbs for two revolutions before breaking. *Let's think about this for a moment... Some have said the Haynes manual requests these narrow bolts be torqued to 89 ft.lbs. Simply I think that is rediculous. My '67 Ford's head bolts are massive (1/2") and they require about 110 ft.lbs each. These bolts are about as big in diameter has the '67's valve cover bolts - those are torqued to 7-11 ft.lbs. each.

Now put the large top-plenum half gasket on. This fits in the lower plenum half in a slot with little tabs too. As I mentioned, it grew. Keep at it and ensure it is equally placed. It is a bit stretchy so it is inclined to not lay just right. Once you get it in place get someone to pry up on the cowling [Blue Line] above the engine and reposition the top half of the plenum. Lift up on the plenum and have someone check the position of the long gasket. Mine popped out once so this brief check is worth it. If it is good lower the plenum top into place. Move it around a bit and eye-ball the bolt holes. Get them close and start the bolts on the four corners. Once started, jiggle the plenum around without lifting it up. This will help center it. Once centered, install the other bolts in the same places they came out of. Some have towers on them that are attachment points for spark plug wires and other stuff.

Using three sequences, tighten down the bolts. Start near the center bolts on the front and back and in a cris-cross pattern back and forth tighten each bolt in turn. When you have tightened them all once, start the pattern over and tighten them a bit more. Do this one final time. Sorry no torque spec! Take heed... this is polycarbonate (or whatever) (hard plastic) not metal. Do not over-tighten these bolts.

*KDS also said that the top plenum bolts have the same torque specs. He and I both recommend tightening them snuggly by hand instead of going off the spec. I suspect the Haynes spec is a misprint and the bolts should be tightened no more than 7-11 ft.lbs. Which by the way, if you divide 89 by 12 you get 7 and change.

Now put on the little u-shaped vacuum line. It was the one with two [Yellow Dots] above.

Next. Put the throttle cables back on. Patience might be needed here. If I had three hands this would have been a breeze. My 17-year old helped again.

Now reinstall the throttle cable mounting fixture. Two bolts will be needed for this.

Next come the PVC tube and valve. Put them back on.

Now put on the negative battery cable and tighten appropriately.

Next check the flasher fluid and exhaust grease. Just kidding.

Clear all tools and rags from the engine compartment. Fire it up. Mine ran great, and still is... no more 171 or 174 error codes. I hope you have the same success as I. Again, P0401 came up later and that was linked to the DPFE as discussed above.

Here's some links for the TSB regarding this matter.

TSB (Part1)
TSB (Part2)
TSB (Part3)
TSB (Part4)
TSB (Part5)

You can right-click on each of these and select Save Target As to get copies of these documents.

BTW: KDS is someone who contacted me with some great advice and suggestions for the information contained herein. His added comments and corrections are much appreciated.

The information contained herein is presented with no expressed or implied warranty or promise with regards to any of its content. Further, if you use the contents shown herein as a guide you could break something if you have much, little or no experience with automotive mechanics. If you chose to continue, you do so at your own risk. I shall not be held liable for any damages caused by your interpretation of this document, references to it, your use of it, or anything you may do either on purpose or accidently to your any anyone's vehicle.