Desperate for advice on P0401 EGR code - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 10-23-2014
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Desperate for advice on P0401 EGR code

I have a '99 Ranger 2.5 and have been driving for months with my check engine light on. The code that it's showing is the P0401 or "EGR flow". I have since replaced the DPFE sensor, EGR and gas cap for good measure and I'm still getting the code. What else am I missing that could be related to this code? I usually don't blindly replace parts unless I know they need replaced, but I figured there are only two or three parts related to this code all of which I can replace fr under $100.
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Old 10-23-2014
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Factory DPFE sensors need to be replaced at around 80k miles, after market seem to last longer, so probably not a waste on money replacing that with P0401 showing.

EGR valve can usually be cleaned if it was dirty, and then just put a vacuum hose on it and suck on it to see if valve opens and closes to make sure it works.
Also make sure tube to exhaust manifold is clear.

The other part of the EGR system is the modulator, this is an electric valve the computer uses to increase vacuum at the EGR valve to open it.
If you follow the EGR valve vacuum line it will go to the Modulator.
Modulator will have a second vacuum line that goes to the intake manifold(the vacuum source).
Make sure both of those vacuum hoses are hooked up and in good condition.


The DPFE sensor has two pressure hoses, both hook to the exhaust manifold, one is near the EGR valve's tube, one is farther away.
When computer opens EGR valve the pressure in the exhaust manifold changes more near the EGR tube, the DPFE(differential pressure feedback) sensor measures that change, this is how the computer tells the "EGR flow".

Low flow could mean one or both of the pressure hoses are plugged, because pressure isn't changing enough when computer opens EGR valve.
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Old 10-23-2014
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Quote:
Originally Posted by RonD View Post

EGR valve can usually be cleaned if it was dirty, and then just put a vacuum hose on it and suck on it to see if valve opens and closes to make sure it works.
Also make sure tube to exhaust manifold is clear.
I appreciate the quick response Ron. Is it safe to say I can return my new EGR and put the old one back on (it was cleaned with carb cleaner) since it seems it may be related to the hoses you mentioned. I'll give those a look when I have some daylight tomorrow.

In regards to cleaning an EGR, what's the proper way to do so?

Thanks in advance.
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Old 10-23-2014
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Carb cleaner is fine, anything that loosens the carbon build up, but keep it out of the vacuum chamber.
And test it when cleaned and dried out.

One other thing, any time you change or clean something on the engine and especially if there was a code and/or CEL(check engine light), you need to reset the computer, clear the CEL.
Scanner can do that, or unhooking the battery for 5 minutes.

What this does is reset the computer so it will "relearn" the settings for any new or cleaned parts.
It is also a helpful tool if engine is cold for the restart.
Only a few sensors and controls are used until engine warms up, so if you time how long it takes before CEL comes back on you can narrow down where a problem might be.
EGR system, for example, is only used when engine is under load, valve is closed most of the time.

Ford Brand DPFE sensor is an exception, it does wear out, but most sensors and controls last the life of the vehicle.
Sensors are the "messengers", and the old saying "don't shoot the messenger" applies.
Codes are generally a mechanical issue warning, the working sensor detected the problem, so.............don't shoot the messenger, lol.

And there are specific codes for a bad sensor, computer tests sensors all the time, a sanity check, if sensor fails a code will come up for that failure.
It isn't a fool proof system, because God always makes a better fool, but it does work pretty well for what it is.
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