I've cleaned the throttle body entirely, replaced the EGR valve, replaced the DPFE sensor, replaced the hoses from sensor to EGR pipe, cleaned EGR pipe, so I'm thinking I've pretty much replaced/cleaned the entire EGR system and I STILL keep getting the P0401 EGR "insufficient flow" engine light error code - what's the deal?!! I've also checked the cable connected to the sensor and am getting appropriate resistance/voltage. I'm all out of ideas - anyone else???
Thanks in advance!
p.s. I've got a '98 F-150 w/ 5.4L, just rolled 100k.

 

did u check all the vacume lines and tried clearing the codes at the dealership they dont just go away u know....u gotta take ti to dealership and have the codes cleaered

 

I am also curious if you replaced your vacuum hoses, and checked them with a vacuum gauge.

If you don't have a scan tool, reset your ECM by disconnecting the negative battery cable and then turning on your headlight switch for a few minutes. Then turn the switch off, and reconnect the battery cable. This will drain any capacitors retaining codes in memory.

 

Ya, I cleared the codes after every step of trying to solve the problem - I know it doesn't just go away itself! After a few miles it comes right back on again. It must be a vacuum line or something, but never heard of this problem being so persistent, especially cleaning and replacing everything that I have - thanks anyway for trying.

 

Well, the valve itself is operated by engine vacuum, so if there is a problem with the vacuum line or it's source, it won't matter if you replaced everything else. Confirm with a gauge that the vacuum line has vacuum in it.

 

I had a problem with the EGR valve in my old Ranger. I got fed up with it and just took it to the shop.

 

Well, the engine runs like a top and I'd think if the valve wasn't working properly I'd have some idle problems at least. I can give it a try, tho - thanks!

 

How do you know it's the same code again? May be a different one.
A 401 code won't come back on in just a few miles.
It take at min. 3 full drive cycles 'after the 401 is cleared' for a 401 code to set and light again.
Here the way it works.
After the engine is fully warmed and 'other EGR tests performed', the PCM requests the EGR be opened a certain percentege by using pulewidth modulation. This only happens once per drive cycle.
Then the DPFE measures the pressure differential across an orfice between the two small stand pipes as gas is flowing through to the opened EGR valve. This has to happen 3 times before the PCM concludes there is a failure if the DPFE does not return the correct signal readings each time. This is an emmissions test only.
The reasons for three test sequences is because in winter and at freezing temps, there can be frozen moisture in the EGR tube that would block the passage of gas, so there is no instant failure code generated until a fair amount of testing and engine heat is generated each time before assuming the tube is non functioning.
Question is is the vacuum gate valve controlling the vacuum to the EGR fully functional?
Do a search for a post on servicing a 401 code for more info on how the test the system parts for function.
Then read for code again to be sure what code/s you should be chaseing.
You are at a disadvantage not having a scanner and knowing how the systems are supposed to work. It becomes costly to keep buying parts.
Note that the DPFE for a 5.4 is a different part number than for a 4.6. Is the right one on your truck?
Good luck..

 

I know it's the P0401 code each time - I take it to AZ where they hook up their computer and get the code (and it's the only one - I have them clear it each time or I disconnect battery, run lights, etc...). Ya, it usually takes several miles to set off the light again. Like I said, the truck runs great, so the only reason to mess with it is to get that stupid light to turn off (and pass inspection) but I've got a while. Thanks for all the great information posted - I'll look into the vacuum issue next.

 

Try replacing your PCV valve. I had this problem and it fixed it. SO FAR...

 

jwagold,
I just cleared a 401 fault on my 02.
I have documentation on how this works and it does work as defined.
I cleared my code several times and it took 3 full and seperate drive cycles to come back on, each time.
My PCM works no different than yours. The lines in the programs work the same for all models and this peticular function.
I can refer you to this info if you feel it would be of benifit.
I hate to disagree with you but I think you are missing something is why you can't get the problem cleared.
All there is to it is the PCM, the DPFE, the EGR, the EVR, wiring, hoses and exhaust metal tubeing and how the routine is invoked.
Good luck with it.

 

The 401 on my 97 5.4 was caused by cracked vacuum lines behind the battery. The cracked line was the supply for the EGR vacuum relay.
With the engine running pull off the vacuum fitting on the relay.. Feel the supply side with your finger. There should be enough vacuum to very firmly stick your finger to the hole and raise a little red ring on your skin. If you can barely feel the vacuum , check for leaks. Another check would be to jumper the supply side of the fitting to the egr side of the fitting, while the engine is running. This should cause the egr valve to go to full open and stall the engine very quickly.
You could go high tech and use a vac gauge in lieu of the finger test, but wheres the fun in that.

Good luck..

 

Party pooper. lol.

 

Lately, I've seen a lot of people put the hoses on the DPFE backwards and continue to get code 401. There's a big input and a small input to the DPFE. The big input may be on the right on your old sensor, but it might be on the left on the new sensor.

The hoses look the same, but they have different fittings at the ends. Take off the hoses and connect the big nipple on the exhaust pipe to the big input on the DPFE with the hose that has the bigger fitting.

I know it sounds silly, but I see this all the time on 4.6L engines.

 

Ok, when I get a chance I'll check the vacuum lines and I just so happen to have a new pcv laying around I can throw in there for grins (if that fixes it I'll be slightly annoyed) Thanks for all the tips - I'll let ya know if/when I get 'er fixed.