I have a 1999 F150 with a 4.6 engine and my Service Engine Light came on recently. I went to Autozone and they came up with two codes - PO401 and PO133. They said it could be the EGR Valve, the EGR Pressure Sensor or both. I have heard that it could be just carbon build up or cleaning the sensor. My problem is that I have no idea where the EGR Valve or the EGR Pressure Sensor are located. Does anyone know where there is a 4.6L engine diagram on the net that shows their position and am I on the right track, given the two codes that came up?

 

P0133 is the passenger side front O2 sensor. It is too slow to rerspond so it set a code. The leading casue is a contaminated O2 sensor.

P0401 is for insuffecient EGR flow. Cleaning the ports should help. It certainly will not hurt. It could also be a faulty D.P.F. EGR sensor.

I would Check for vacuum leaks, re: P0133. If I had close to or more than 60,000 miles on the O2 sensors i would change them and clean the EGR passages re: P0401. Reset the Codes, disconnect battery negative cable for a minute and reconnect. Drive it till codes reappear and go from there.

Regards

Jean Marc Chartier

 

The PO401 is EGR Flow Insufficient Detected. You probably have clogged ports on your Throttle body plenum( the elbow that connects the TB with the intake. Thats where I would start first you have to remove the elbow and TB and clean out the ports with a Throttle body cleaner. Do not use carb cleaner. Your EGR is also connect to this body, you will want to put antiseize on the threads before reconnecting. And purchase a new intake gasket for the elbow and egr gasket.

The PO133 is a O2 sensor circuit slow response Bank one sensor one. I would replace both up stream O2 Sensors. Given the year of your truck. A 22mm open end wrench and hose them down with wd40 before you start. Put antiseize on them when you reinstall. Disconnect the negative batter cable before you start. The one on the driver side is the hardest one to remove. The passenger side is easier is you remove the tire and plastic wheel well cover.

Hope this helps

 

Mdelano & JMC,

Thanks for posting your replies. I have had the PO401 code flash several times in the past fewl months and thought it was simply a case of bad gas. I have over 92K miles on my 98 4.6 and have noticed a considerable decline in MPG since adding headers and a CAT-Back which I thought would actual improve the MPG. Actually, the PO401 code first flashed about this time as I recall now. Maybe part of my problem is that I have never changed the O2 sensors as JMC pointed out. Should I only replace the up stream O2 sensors as Mdelano mentioned and are these the ones forward of the CATs? I didn't realize until I looked under my truck this morning that there are 4 O2 sensors. Do I need to replace all four?

 

crain,

Only the front two sensors need changing.

JMC

 

JMC...again, thanks much. I continue to learn alot about our trucks on this board.

 

Crain

I would try to clear the 401 code before replacing O2 sensors.

A vacuum leak in the EGR control circuit , check behind the battery for the most common place, can cause the 401 any may cause a lean 02 sensor.

401 insufficiant in a high mile 4.6 is very commonly caused by clogged ports in the manifold. This can also cause a decrease in power and milage. Do a search on p0401 and you will find lots of info on what to look for , including pictures, and how to clean them.

 

This site has some good info on trouble codes, including those ones: https://www.obd-codes.com

 

Guys...thanks for all the advise.

I am going to do the conservative thing first and clean the throttle body and ports. It just seems to me that this could be done without removing the TB or is removing the TB the recommended way to ensure all the gunk is removed?

 

Remove the TB and Elbow from the intake. No need in seperating the two.

 

Boy...I hate to ask this question because it will show just how mechanically I am "not inclined." What intake gasket (specific name) do I need to replace?

I read the post with pictures and instructions on removing the throttle body and throttle body elbow. The instructions state to replace the intake gasket and egr valve gasket. I assume that was all the parts guys needed to know to order the gasket. Well, it wasn't...when I asked for an intake gasket, the questions started. Is it the upper or lower TB? I thought the TB was the TB? Is what everyone calls the TB elbow considered the lower TB? Then, I was aked if I needed the gasket for the spacer between the manifold and TB? I wasn't aware there was a spacer. I thought the TB sits on the elbow and the manifold or lower intake? Anyways, I told the parts guy to order the gasket for the lower intake or top of the manifold where the TB and elbow sits? Is this right? Eitherway, I will know for sure once I get my truck from my son and remove the parts and compare the gasket with what comes in tomorrow...nope, they did not have the gaskets in stock.

 

EDIT: Spelling
Sometimes you can get away with reusing the gasket. Just so you can see what is involved. #2 is the Throttle Body
#3 is the Throttle Body gasket
#4 is the Throttle Body adapter, we call it the elbow
#12 is the Throttle Body adapter gasket
#18 is the Intake Manifold upper.
#19 is the Intake Manifold gasket, lower
#21 is the Intake Manifold Lower
#22 is the Intake Manifold gasket, upper
You need 2 of them they seal the manifold to the heads.
#10 is the EGR valve
#9 is the EGR valve gasket
#6 is the IAC
#7 is the IAC gasket. On the 5.4 it is at the rear of the elbow.

JMC

 

JMC,

You are my hero...thanks a million. A picture for me is worth a million bucks. I got the parts off--well almost. Remember the detail post with picture and a little humor on how to remove the TB and clean it. The guy that wrote the article talked about how tight the bolt is that holds in the "flying spacer". The bolt is tight for sure, I broke two cheap 10mm shockets trying to remove it, borrowed my neighbor's Craftman (unbreakable socket) and started to remove the bolt, and it turned for a while and eventually the bolt broke off inside the TB. Well now, what do you suppose I said to that....

 

I cleaned the EGR ports this morning on my '97 4.6. It spit a p0401 code a few weeks ago. Sure enough, the ports were completely crudded up. The whole job took about four hours, not including the trip down to the dealer for two little gaskets (TB elbow and EGR $13. - sheesh!). A good hour of that was cleaning up the ports and the TB itself, but I'm **** about these things. I wouldn't tolerate a spec of black in the passages or a crumb of old gasket on the TB and EGR surfaces.

It is true that you don't need to remove the EGR valve from the pipe - just leave it in place; remove the two 10mm bolts and pull the TB & elbow away from it. This is a good thing because I didn't have an open end wrench that big anyway! Although I must say that the rear 8mm bolt for the TB elbow is a pretty tight fit to get at under the firewall... but do-able. The only thing that really drove me nuts was getting the hose clamp back on the vacuum hose to the brake booster. Those factory spring clamps are hard enough to reconnect when you're not trying to reach it tucked back in behind and underneath everything. I should have just replaced it with a real stainless screw clamp.

Code's gone; truck and owner are happy campers