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I have a 2000 Ford Focus, SOHC engine.

I've had this code on for a while, maybe for a year now. No typical symptoms though. In April I replaced the EGR valve and the EGR tube, thinking that there might have been carbon build-up in the tube or the valve was done. This didn't help.

After reading the forum I figured that DPFE sensor failure is the most common cause of this code. Replaced it yesterday, after 50 miles of driving the code came back up again, so that wasn't the issue.

So, I'm confused right now. Basically, the whole system is brand new - the valve, the tube, and the sensor. I'm guessing my last resort would be to replace the solenoid.

I tried checking the tube and valve by sucking on the vacuum hose - and it did shut down the engine, so the valve and the tube are fine.

I don't experience any typical EGR malfunction symptoms. The car doesn't idle, buckle or cough, it doesn't shut down the engine at the red lights. It is just the annoying orange light on the dashboard that is driving me crazy.

I would be very grateful for any advice. Most likely I am going to replace the solenoid and pray it will work out. Are there any links on how to replace the solenoid?

Maybe the issue with the stupid car computer that thinks I have a problem with the EGR when I actually don't?

P.S. I don't know if it is important information, but: up until April the car had both Cat-issue and EGR CEL codes on, but I didn't bother since there weren't really any symptoms. When I started fixing it, I saw that the EGR tube was blown in two parts and that was obviously the reason why the EGR light was on. Replacing the tube didn't help though.
 

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I have a 2000 Ford Focus, SOHC engine.

I've had this code on for a while, maybe for a year now. No typical symptoms though. In April I replaced the EGR valve and the EGR tube, thinking that there might have been carbon build-up in the tube or the valve was done. This didn't help.

After reading the forum I figured that DPFE sensor failure is the most common cause of this code. Replaced it yesterday, after 50 miles of driving the code came back up again, so that wasn't the issue.

So, I'm confused right now. Basically, the whole system is brand new - the valve, the tube, and the sensor. I'm guessing my last resort would be to replace the solenoid.

I tried checking the tube and valve by sucking on the vacuum hose - and it did shut down the engine, so the valve and the tube are fine.

I don't experience any typical EGR malfunction symptoms. The car doesn't idle, buckle or cough, it doesn't shut down the engine at the red lights. It is just the annoying orange light on the dashboard that is driving me crazy.

I would be very grateful for any advice. Most likely I am going to replace the solenoid and pray it will work out. Are there any links on how to replace the solenoid?

Maybe the issue with the stupid car computer that thinks I have a problem with the EGR when I actually don't?

P.S. I don't know if it is important information, but: up until April the car had both Cat-issue and EGR CEL codes on, but I didn't bother since there weren't really any symptoms. When I started fixing it, I saw that the EGR tube was blown in two parts and that was obviously the reason why the EGR light was on. Replacing the tube didn't help though.
What where your previous cat and EGR issues? I ask because if your cat was restrictive it would result in enough exhaust backpressure to destroy both the EGR tube and the DPFE sensor.

The DPFE is a common issue because it's exposed to lots of moisture, heat and corrosive exhaust gasses. It sounds like your valve is working properly if you can stall the engine by applying vacuum to it.

The P0401 means the PCM doesn't see a significant increase in EGR flow when it commands the vacuum regulator solenoid to open the valve. Without a vacuum regulator circuit malfunction code your possible causes are:

Resistance in the EGR vacuum regulator solenoid power or control circuit
A bad EGR vacuum regulator solenoid
A hole or restriction in the vacuum line between the solenoid and the valve
A hole or restriction in the vacuum line between the intake and solenoid
* a missing orifice in the EGR tube *

If you put a BRAND NEW tube on it - not likely the orifice is missing. However, the DPFE sensor works by measuring the pressure difference across a restriction in the EGR tube. As the EGR valve opens, intake vacuum is present on one side of this orifice and exhaust backpressure is present on the other side. The more the valve opens, the greater the pressure difference across this orifice. Occasionally, I've seen this orifice rot out and resulting in great EGR flow, but not allowing the pressure difference required for the DPFE to measure the flow. This P0401 code literally means that the DPFE voltage is within normal range (.5v - 4.5v) but it does not increase when the solenoid is commanded to open the valve.

G/L

_Shane
 

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What where your previous cat and EGR issues? I ask because if your cat was restrictive it would result in enough exhaust backpressure to destroy both the EGR tube and the DPFE sensor.
There were no issues per se. I don't think I noticed any difference in engine's behavior after I replaced the cat and the EGR tube and valve. The old cat was the original one and was on there for 11 years. I'm pretty sure it was burnt up. I had a code saying the cat's efficiency was below threshold.

The EGR tube was broken in two. It literally had an opening in the middle. I don't know if it was broken while I was driving it, or if it was very week and broke when I tried to get to it and look at it. I wasn't planning to replace the tube, I just wanted to put in a new valve. (By the way, the old valve was fine, it didn't need replacement, but I had a new part on hand, so I just did it).

Would my car be able to run normally with a hole in the EGR tube?

The DPFE is a common issue because it's exposed to lots of moisture, heat and corrosive exhaust gasses. It sounds like your valve is working properly if you can stall the engine by applying vacuum to it.

The P0401 means the PCM doesn't see a significant increase in EGR flow when it commands the vacuum regulator solenoid to open the valve. Without a vacuum regulator circuit malfunction code your possible causes are:
Vacuum regulator circuit - is it a part of the PCM, or a solenoid?

Resistance in the EGR vacuum regulator solenoid power or control circuit
A bad EGR vacuum regulator solenoid
A hole or restriction in the vacuum line between the solenoid and the valve
A hole or restriction in the vacuum line between the intake and solenoid
* a missing orifice in the EGR tube *
I'm pretty sure there are no holes in vacuum lines. I inspected them very closely. The tube is brand new, so I'm pretty sure the orifice is big enough. It's been 5 months and roughly 5000 miles since I replaced the tube. Would it be enough time for the tube to get clogged?

If you put a BRAND NEW tube on it - not likely the orifice is missing. However, the DPFE sensor works by measuring the pressure difference across a restriction in the EGR tube. As the EGR valve opens, intake vacuum is present on one side of this orifice and exhaust backpressure is present on the other side. The more the valve opens, the greater the pressure difference across this orifice. Occasionally, I've seen this orifice rot out and resulting in great EGR flow, but not allowing the pressure difference required for the DPFE to measure the flow. This P0401 code literally means that the DPFE voltage is within normal range (.5v - 4.5v) but it does not increase when the solenoid is commanded to open the valve.

G/L

_Shane
Again, I'm not experiencing any physical problems that usually come with this code. It looks like the EGR is functioning fine. This is the part that puzzles me the most.
 

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There were no issues per se. I don't think I noticed any difference in engine's behavior after I replaced the cat and the EGR tube and valve. The old cat was the original one and was on there for 11 years. I'm pretty sure it was burnt up. I had a code saying the cat's efficiency was below threshold.
You had a P0420 code then. Makes sense. Cats can either just not do their job or they can become plugged and restrictive. Sounds like you just had a used up cat that wasn't restrictive and an EGR tube that rusted through. Two mutually exclusive issues.

The EGR tube was broken in two. It literally had an opening in the middle. I don't know if it was broken while I was driving it, or if it was very week and broke when I tried to get to it and look at it. I wasn't planning to replace the tube, I just wanted to put in a new valve. (By the way, the old valve was fine, it didn't need replacement, but I had a new part on hand, so I just did it).

Would my car be able to run normally with a hole in the EGR tube?
Your car should run just fine with a small hole in the EGR tube... but because this tube is attached to your exhaust on one end and your intake on the other end - it would act as an exhaust leak when the EGR valve is closed and a vacuum leak when the EGR valve is open. It was likely minor enough to not cause a symptom or, as you suggest, it broke when you where messing with it and was not broken while driving beforehand.

Vacuum regulator circuit - is it a part of the PCM, or a solenoid?
The vacuum regulator circuits are wires that go between the fusebox, PCM and the solenoid. The solenoid has two wires and a vacuum line. One wire is a fused power from the fusebox and the other wire is a ground circuit that is duty cycle controlled by the PCM. Also, you have a vacuum line going to this solenoid from the engine. Another vacuum line goes from the solenoid to the EGR valve. The solenoid also has a black cap on it. Below that black cap is a little filter. Your vacuum solenoid is literally a little controlled vacuum leak. When the PCM wants to open the EGR valve, it sends a duty cycled ground to this solenoid and inside the solenoid it begins to pinch off the "leak". If the vacuum can't "leak" through the little filter, it will begin to "suck" on the line that goes to the EGR valve. As you know, if vacuum is applied to the valve, it begins to open.

So, the PCM indirectly controls the opening of the EGR valve by applying an electrical duty cycle to a device that will regulate vacuum to the valve.

I'm pretty sure there are no holes in vacuum lines. I inspected them very closely. The tube is brand new, so I'm pretty sure the orifice is big enough. It's been 5 months and roughly 5000 miles since I replaced the tube. Would it be enough time for the tube to get clogged?
If the tube were clogged, you would get an "overflow" code, not an "underflow" code. You wouldn't get any actual EGR flow but the sensor would read this huge pressure difference and as a result the computer would "think" it's getting a crapton of flow.

Your P0401 code means the DPFE sensor isn't reacting to the command of the vacuum solenoid. If your tube and hoses are 100% - the only thing that makes sense is electrical resistance in the DPFE signal or VREF circuit, electrical resistance in the vacuum regulator power or control circuit, or a bad vacuum regulator solenoid.

Again, I'm not experiencing any physical problems that usually come with this code. It looks like the EGR is functioning fine. This is the part that puzzles me the most.
EGR doesn't affect driveability if it isn't working, so I'd imagine the "no flow" code is accurately reflecting the fact that you have no EGR flow. If it where disabled you'd never know. It only works under light load accel and cruise. It's completely disabled at idle and under WOT. You simply aren't meeting NOx emissions if the system doesn't work so that's why your light is on. Frankly, it won't do much more than give you a tad worse fuel mileage and contribute to smog formation[rolleyes].

I hate to tell people to chuck parts at a car but replacing the vacuum solenoid is the easiest way to figure this one out from here. I could tell you how to test the wires properly but I don't know what your knowledge level is for DC circuits and I doubt you have a multimeter and a load tester. Try a solenoid and if it doesn't help I'll get more specific if you'd like.
 

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First, thank you so much for all this detailed information.

I hate to tell people to chuck parts at a car but replacing the vacuum solenoid is the easiest way to figure this one out from here. I could tell you how to test the wires properly but I don't know what your knowledge level is for DC circuits and I doubt you have a multimeter and a load tester. Try a solenoid and if it doesn't help I'll get more specific if you'd like.
It is funny that we came across DC circuits, but I actually do have some basic knowledge about those. I will be starting my Electrical Engineering classes this coming fall. So far I've taken intro to circuits. I know how basic elements such as resistors, batteries, capacitors, inductors, op-amps, etc. work. I have a multimeter on hand. I might be able to get a load tester from a friend.

I checked with a local car parts store and they have a solenoid on hand for $27. It comes with a 2-year warranty and I'm pretty sure I'd be able to return it and get my money back if it doesn't fix the issue. So my plan is to replace the solenoid later tonight. I hope it will resolve the issue.

If it doesn't - I'll take off the air intake and will examine the EGR tube closely, will make sure there are no leaks at the gaskets. I'll check the resistance on different cables going to the solenoid and I'd be glad to start testing the circuit to identify the part of it that is causing trouble.

Again, thank you for your help. I will write back later tonight after I replace the solenoid and drive around for some time.
 

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First, thank you so much for all this detailed information.



It is funny that we came across DC circuits, but I actually do have some basic knowledge about those. I will be starting my Electrical Engineering classes this coming fall. So far I've taken intro to circuits. I know how basic elements such as resistors, batteries, capacitors, inductors, op-amps, etc. work. I have a multimeter on hand. I might be able to get a load tester from a friend.

I checked with a local car parts store and they have a solenoid on hand for $27. It comes with a 2-year warranty and I'm pretty sure I'd be able to return it and get my money back if it doesn't fix the issue. So my plan is to replace the solenoid later tonight. I hope it will resolve the issue.

If it doesn't - I'll take off the air intake and will examine the EGR tube closely, will make sure there are no leaks at the gaskets. I'll check the resistance on different cables going to the solenoid and I'd be glad to start testing the circuit to identify the part of it that is causing trouble.

Again, thank you for your help. I will write back later tonight after I replace the solenoid and drive around for some time.
Good deal man, I'll keep an eye on the thread and try to help any way I can.
 

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Good deal man, I'll keep an eye on the thread and try to help any way I can.
Replaced the solenoid about an hour ago. Drove 20 miles after, so far no code. The scanner showed that the computer ran the EGR test already, but I'm not getting too excited yet. Last time the light came up after about 50 miles. Tomorrow morning I will drive about 25 miles on the highway so I'll see if the light comes up.
 

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Anytime I touch something electrical on my Focus I disconnect the - neg side of the battery until the work is completed and then put it back on when I'm done so the ecu can relearn all the parameters and make the adjustments it needs to run like its suppose to.

I know you need the current on to test things out , I'm referring to when and during your replacing parts .
 

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Anytime I touch something electrical on my Focus I disconnect the - neg side of the battery until the work is completed and then put it back on when I'm done so the ecu can relearn all the parameters and make the adjustments it needs to run like its suppose to.

I know you need the current on to test things out , I'm referring to when and during your replacing parts .
Thanks for the advice. Will keep that in mind for future.
 

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It must have been the solenoid because the light didn't come back after 150 miles of driving.

I sold the wagon today, but should get a liquid grey metallic 2003 zx3 at the end of this week.
 

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Mine too has p0401 code and I just put dpfe on it and was waiting to see if the light would go out on its own and in the meantime, my battery took a dump on my yesterday leaving me on the side of the road in 106 degree heat waiting on my dad to bring me a new battery. Now i have no check engine light since i put the battery in but I will be doing an obd drive test to set all the codes tonight. Lets hope this thing will pass emissions.
 

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Mine too has p0401 code and I just put dpfe on it and was waiting to see if the light would go out on its own and in the meantime, my battery took a dump on my yesterday leaving me on the side of the road in 106 degree heat waiting on my dad to bring me a new battery. Now i have no check engine light since i put the battery in but I will be doing an obd drive test to set all the codes tonight. Lets hope this thing will pass emissions.
I don't know how often the PCM runs the EGR test, so whenever I replace part that might fix the CEL issue I reset the codes. Also, above there was a very valuable advice to take the cable off the negative terminal of the battery every time you work on the electrical in your car.

Good luck with you p0401!
 
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