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.

 

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.

 

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.

 

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.

 

I pressure tested EGR valve it held the pressure. That means the EGR valve is good? right correct if wrong. i put a volt meter on the feed wire DPFE it said 1.5 volts, put pressure on the EGR valve and thengine sounded like it was going to stall and the volts went up like 3 volts, released the pressure and went back down to 1.5 volts. How I tested the solinoid it had like 14 volts, took hoses off and there was pressure out of one of them, which tells me the solinoid is good. After doing this I cleard the code P0401. Drove like three miles to Auto Zone they check the codes and there wasnt any. Today I drove about 5 miles and now the engine light came back on and the truck sounded like it was trying to spit something out the engine sounded like it was going to stall than it leveled out and I got home!!! WHAT CAN THIS BE!!!

 

Hoses on the DPFE can not be reversed

EGR solenoid gets voltage with key on(red wire), but has no ground so doesn't open, the computer pulses the ground to it to apply a little or alot of vacuum to the EGR valve

 

I got home and the check engine light was on again. So I checked the codes again now its a P0402 code. Thats opposite of P0401, so even though the dpfe is reading the right volts do you think it could be the DPFE sensor because that regulates the amout of gas, correct if im wrong

 

Engine OFF, Key ON
There are 2 types of DPFE sensors, aluminum and plastic

DPFE sensor should have Brown/light green stripe wire
Use a sewing needle to pierce that wire to test its voltage
Aluminum should read .40 to .60volt
Plastic .9 to 1.1volt

Then test voltage on Brown/white stripe wire, should be 5volts, this is the power wire
If this wire is 5volts but brown/green is not between .4 and 1.1 volt then DPFE sensor is bad, regardless of the type

The Grey/red stripe should be a Ground, but a reference ground, so may not be 0 ohms to engine ground

 

I had the medal one that I replaced about a year ago. I replaced it with the plastic one. I tested the brown/light green wire it read 2.3 volts I replaced it with another plastic on from advanced auto, last Sunday. It drove great all week, today I put the defroster on. At the light with the brake on rpms kept going up like it wanted to take off. Pulled into the parking lot at work noticed the check engine light on. Worked all day coming home it kept the defroster and fan off, was stopped at a few light with the 5 :00 traffic, rpms stayed steady. P.S. Saturday I got in the truck and the time and all radio stations were erased, didnt think to much of it because I cant shut the radio off without shutting off the key, and there was no check engine light and was driving good. Could this be a short or a relay,

 

Check DPFE sensor signal voltage on a scantool or at the sensor, key on engine off, and make a note of it. Then start the truck and see if the voltage changes. It should stay almost exactly the same. If it doesn't, you have EGR flow at idle and shouldn't. This would make it run rough.

Now rev the engine to 2500 or so, and the DPFE voltage should increase considerably. Probably in the 3 to 4 volt range. Never more than 4.5 volts, ever.

When the DPFE sensor fails, it's usually catastrophic, not a little bit. If you rev the motor up and DPFE voltage doesn't really change, then chances are you either have a vacuum line issue in the EGR system somewhere, or you have clogged EGR passages in the intake manifold, or the valve is carboned up and stuck shut.

 

Now I got two new codes, P1444 and P0171. Going to get mass air flow sensor cleaner. Purge flow sensor is about 20.00. When I get them done this weekend I will update you. Let me know if there is anything else I should do. Thank You in advance!!!

 

The purge flow sensor is really easy to diagnose. Turn the key on, and check DPFE voltage, and note it. Then turn the truck on. It should be almost exactly the same voltage. Then rev it up, and the voltage should increase.

It's usually either 0.5 to 1.5 volts key on, engine off, in my experience. But that could vary a little. Revving the motor up could get you up in the 3 volt range. Driving it could put it up in the 4 volt range at cruise speeds. Closed throttle should bring it right back to the same voltage as idle and engine off was.

P1444 FORD - Purge Flow Sensor Circuit Input Low
This code indicates the DPFE signal voltage is lower than expected. This might be an unplugged sensor, broken signal wire, signal wire shorted to ground, bad DPFE, or broken 5v VREF power source.Check DPFE VREF with key on, engine off. Should be 5 volts. There may actually be two wires that have 5 volts with key on, engine off, unplugged, so be sure to only check the VREF voltage on an unplugged sensor. The other 5v is sort of false. It's the signal wire, which will get pulled down towards ground voltage once you plug the sensor in.

 

I have a leak in the fuel filler neck, when I fill up it will pour out on the ground. Can this problem create a P1444 code,

 

Yes, it would cause an EVAP code since gas tank is no longer air tight

 

Thank You for the advice RonD. I changed the fuel filler neck 4/19 good friday. I cleared the codes, by tuesday the check engine light came back on. P1444 code came up. Purge flow sensor circuit input low. Good news is I filled up with gas today and no leaks!!!

 

Good work


In 1995 the charcoal canister for EVAP system should be in the engine bay on rad support

It will have a vacuum hose that runs back to the gas tank and another vacuum hose that runs to the intake manifold

On the hose that runs to the intake manifold there should be a Pressure sensor and a solenoid valve

After you start the engine and drive a bit the computer will use(open) the solenoid to apply vacuum to the gas tank, then close solenoid to see if the system(gas tank and canister) hold vacuum pressure, by reading pressure sensor's pressure
If its not holding pressure then it will set a code


Inspect the visible vacuum hoses for any leaks

Make sure gas cap seals the tank