Dreaded P0401
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Dreaded P0401
I have thge DREADED P0401 Disease!!!!
The statistics:
1997 F-150 XLT 4X4 Automatic Transmission.
4.6 "W" Engine with 203,000 miles, and I believe the original O2 sensors.
Last November, just in time to need my emissions testing to get my license plate renewed, I got my first ever CEL. Took it to Autozone, read as P0401. Then took the following steps to correct it.
1. Cleaned the EGR Ports in the throttle body, and boy, they needed it.
2. Replaced the EGR valve (stupid, I know I pulled a vacuum on it and the engine stumbled as it should have)
3. Replaced the DPFE Sensor with an aftermarket one, (I started reading the forums about then).
4. Pulled the stainless steel dpfe tube and checked it for cracks or damage, none found.
5. Replaced the EGR Solenoid.
6. Pulled the vaacuum reservoir and tested it. It's airtight and good.
Still no joy, but I found the tube to the PCV valve had a LARGE hole in it, replaced it and all was well. I had since purchased my own code reader by this time. I passed the emissions test, and was happy, for a while.
Two months ago, like a bad dream, it came back.
I went to Ford and got a FOMOCO DPFE ($120,Ouch) and put her in.
Nope, still there.
Put in the original solenoid to see.
Nope, still there.
Replaced the TPS.
Nope, still there.
Cleaned the MAF
Nope, still there.
This is getting expensive, but look at all the spares I'm collecting.
So, this weekend, I put two vacuum gages on the truck and took it on a 70 mile drive to see my Dad for Father's day. An interesting thing showed up.
One vacuum gage was on the line to the EGR valve, the other on the supply line to the Solenoid.
The supply to the solenoid varies with engine speed somewhat and with throttle position as you'd expect. But.... At first the vacuum to the EGR valve varied with throttle, as long as you're not at the idle position on the TPS, just as you'd expect. But after a few miles the vacuum just stopped, and if you hit read on the code reader after a few more miles, sure enough, you see a pending P0401 code. Stop and idle for a couple of minutes, and the vacuum to the EGR starts behaving again for a few miles and quits again. Keep driving and you get a CEL on the same code.
Does anyone here think it might be an O2 sensor?
1. Look at all I've eliminated above.
2. The O2 sensors have 200K + miles on them.
3. This morning, I still had the vacuum gage setup still on the truck and tested it on the way to work with a "cold" engine. All the previous testing was on a "hot" engine.
I had "good" vacuum input to the EGR for about 13 miles of continuous highway driving before the vacuum shut down. Seems like it takes a while to get everything really hot to fail. I have read here and in the Haynes/Chilton guides that the MAF, TPS and O2 sensors play a part in generating a signal to the EGR solenoid. Also, a while back a Ford tech I see at the mall food court occasionally said O2 sensors could cause this and not throw a code. He has advised me on a few other items ( I changed my own heater core) and he's has seemed to be correct in the past.
I think that something is sending a signal to the solenoid to shut down the vacuum to the EGR valve. I just don't know why. I plan to wire a voltmeter to the solenoid next to see if the voltage to it goes away, shutting down the vacuum signal.
I'd appreciate any ideas or suggestions on this. I swear I hate the thought of paying $85/hour to the dealer. I've got till the end of November, but I'm determined to conquer this.
Thanks for reading. If I fix it I promise to update this thread.
The statistics:
1997 F-150 XLT 4X4 Automatic Transmission.
4.6 "W" Engine with 203,000 miles, and I believe the original O2 sensors.
Last November, just in time to need my emissions testing to get my license plate renewed, I got my first ever CEL. Took it to Autozone, read as P0401. Then took the following steps to correct it.
1. Cleaned the EGR Ports in the throttle body, and boy, they needed it.
2. Replaced the EGR valve (stupid, I know I pulled a vacuum on it and the engine stumbled as it should have)
3. Replaced the DPFE Sensor with an aftermarket one, (I started reading the forums about then).
4. Pulled the stainless steel dpfe tube and checked it for cracks or damage, none found.
5. Replaced the EGR Solenoid.
6. Pulled the vaacuum reservoir and tested it. It's airtight and good.
Still no joy, but I found the tube to the PCV valve had a LARGE hole in it, replaced it and all was well. I had since purchased my own code reader by this time. I passed the emissions test, and was happy, for a while.
Two months ago, like a bad dream, it came back.
I went to Ford and got a FOMOCO DPFE ($120,Ouch) and put her in.
Nope, still there.
Put in the original solenoid to see.
Nope, still there.
Replaced the TPS.
Nope, still there.
Cleaned the MAF
Nope, still there.
This is getting expensive, but look at all the spares I'm collecting.
So, this weekend, I put two vacuum gages on the truck and took it on a 70 mile drive to see my Dad for Father's day. An interesting thing showed up.
One vacuum gage was on the line to the EGR valve, the other on the supply line to the Solenoid.
The supply to the solenoid varies with engine speed somewhat and with throttle position as you'd expect. But.... At first the vacuum to the EGR valve varied with throttle, as long as you're not at the idle position on the TPS, just as you'd expect. But after a few miles the vacuum just stopped, and if you hit read on the code reader after a few more miles, sure enough, you see a pending P0401 code. Stop and idle for a couple of minutes, and the vacuum to the EGR starts behaving again for a few miles and quits again. Keep driving and you get a CEL on the same code.
Does anyone here think it might be an O2 sensor?
1. Look at all I've eliminated above.
2. The O2 sensors have 200K + miles on them.
3. This morning, I still had the vacuum gage setup still on the truck and tested it on the way to work with a "cold" engine. All the previous testing was on a "hot" engine.
I had "good" vacuum input to the EGR for about 13 miles of continuous highway driving before the vacuum shut down. Seems like it takes a while to get everything really hot to fail. I have read here and in the Haynes/Chilton guides that the MAF, TPS and O2 sensors play a part in generating a signal to the EGR solenoid. Also, a while back a Ford tech I see at the mall food court occasionally said O2 sensors could cause this and not throw a code. He has advised me on a few other items ( I changed my own heater core) and he's has seemed to be correct in the past.
I think that something is sending a signal to the solenoid to shut down the vacuum to the EGR valve. I just don't know why. I plan to wire a voltmeter to the solenoid next to see if the voltage to it goes away, shutting down the vacuum signal.
I'd appreciate any ideas or suggestions on this. I swear I hate the thought of paying $85/hour to the dealer. I've got till the end of November, but I'm determined to conquer this.
Thanks for reading. If I fix it I promise to update this thread.
Thread Starter
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Freshman User
Joined: Nov 2004
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Originally Posted by ranger88a
There is a filter on the top of the vacuum solenoid. Try cleaning it.
I have already replaced the solenoid with a FOMOCO new, out of the box unit and no joy.
Postmaster
Joined: May 2002
Posts: 3,241
Likes: 3
From: Broken Arrow, OK
It's not the O2 sensors. The only way for that code to set is if the PCM doesn't see enough voltage from the DPFE sensor to believe it's getting all the EGR flow it needs. From my observations the code will set anytime the PCM is forced to request full EGR flow but still doesn't see full voltage from the DPFE sensor.
From what you are describing, I would say that you have a problem with a vacuum line leading to the reservoir. Does your AC default to defrost anytime you are at high throttle for a prolonged period of time? The vacuum lines are affected by heat just like everything else. The cluster behind the battery is known for wierd problems.
From what you are describing, I would say that you have a problem with a vacuum line leading to the reservoir. Does your AC default to defrost anytime you are at high throttle for a prolonged period of time? The vacuum lines are affected by heat just like everything else. The cluster behind the battery is known for wierd problems.
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Originally Posted by Silver Streak
It's not the O2 sensors. The only way for that code to set is if the PCM doesn't see enough voltage from the DPFE sensor to believe it's getting all the EGR flow it needs. From my observations the code will set anytime the PCM is forced to request full EGR flow but still doesn't see full voltage from the DPFE sensor.
From what you are describing, I would say that you have a problem with a vacuum line leading to the reservoir. Does your AC default to defrost anytime you are at high throttle for a prolonged period of time? The vacuum lines are affected by heat just like everything else. The cluster behind the battery is known for wierd problems.
From what you are describing, I would say that you have a problem with a vacuum line leading to the reservoir. Does your AC default to defrost anytime you are at high throttle for a prolonged period of time? The vacuum lines are affected by heat just like everything else. The cluster behind the battery is known for wierd problems.
I have pulles a vacuum on the reservoir and it is OK. I just drove it 25 miles with one vac gage on the input to the egr valve and one gage on the supply line to the Solenoid.
The solenoid is getting PLENTY of vacuum. If I let the truck idle, as in at a long light, the vacuum to the egr comes back for about a half mile or so. Then it abruptly shuts off and will not return till you let the engine idle for a minute or two. I know that the Cylinder head temp sender, TPS, MAF and Cam Pos sensor also play a part in what the PCM calls for. I see your point regarding the output from the DPFE, but I really don't know what else that is directly in the EGR system to look at except maybe the wiring harness to the DPFE and EGR solenoid.
Thanks for the help.
Postmaster
Joined: May 2002
Posts: 3,241
Likes: 3
From: Broken Arrow, OK
OK, I thought you meant you had good input to the EGR solenoid, not the valve. If it's to the valve you need to put a DVOM in parallel with the EVR solenoid and see if the PCM is commanding erratic vacuum, or if it's just happening. You can also probe the middle wire on the DPFE sensor to see what kind of voltage you are getting while the EGR is operating. You should see between 2.5-3 volts cruising on the highway.
When you said it abrubtly shuts off it got me to thinking. When the PCM detects a problem with the EGR system, it turns it off until you stop and it "resets" itself. I think that is what you are seeing.
What condition are the DPFE hoses in?
I think it is time to take a step back and reevaluate the entire system. Here's the process I use at work to diagnose Ford EGR problems. Bare in mind that I'm looking at a scanner when I do this, so if something isn't clear it's probably because I've told you what I would be doing instead of what you should be doing.
1. Determine if the problem is on the "hot" or "cold" side. I define the hot side as anything that touches exhaust gases or the pressures they create. The cold side is everything else. To determine if the hot or the cold is causing the problem, apply vacuum to the EGR valve with the engine idling.
2. If the engine begins to run rough or dies you know that there is flow, but is it enough and is it being measured? You can check this with a DVOM connected between the center terminal of the DPFE connector and ground. You should be able to generate and measure at least 4 volts of flow. You will have to rev the engine a little to measure the max. flow; 1500 rpm should do it. If it passes this test, your problem is on the cold side. I'll cover cold side in a minute because a problem on the hot side is more likely.
3. If you didn't get 4 volts, how much did you get? The DPFE sensor typically either works or it doesn't. I have installed several that were bad out of the box, even Motorcraft, so your new one might not be doing the job. If the DPFE sensor voltage started going up, but then stopped before it got to 4V you more than likely have a restricted EGR passage somewhere. The passages in the intake are not easy to clean thoroughly. Even though you already did that, I would revisit them just to be sure. You can block the throttle open with something and put a mirror in the TB and actually see the ports. Some creative tweaking of a coat hanger will allow you to clean from both ends of the passage without removing the intake elbow. Just cleaning from the outside won't do the job since the passages have a 90 degree bend in them. After this, repeat step 2 and it will probably pass that test.
4. If the DPFE voltage didn't change at all, but the idle quality did, you need a new DPFE sensor or the hoses to it or both. You can replace the stock hoses with vacuum line for testing purposes, but they won't last long enough to be a permanent repair. I should also point out that it is possible that the harness connector at the DPFE sensor isn't making a good connection. It's rare, but it happens.
Cold side:
5. If all the tests above were passed, you have a problem on the cold side of the system. This includes the vacuum supply lines, EVR solenoid, wiring, and PCM. It sounds like the vacuum supply is good to the EVR. To test whether the PCM is requesting EGR flow or not, measure the voltage across the EVR terminals with a DVOM while driving. If it is commanding EGR flow and not getting it, the PCM will eventually quit trying as you have seen. If that's the case, there is something in the system that it really doesn't care for, and it's probably on the hot side.
6. If the PCM is not stopping EGR flow, the problem is either the EVR solenoid or the wiring to it.
There is a lot of gray area in diagnosing this code and there is also quite a bit of gut feeling involved. I think the above process will lead you to an answer, but it may or may not be an easy find.
When you said it abrubtly shuts off it got me to thinking. When the PCM detects a problem with the EGR system, it turns it off until you stop and it "resets" itself. I think that is what you are seeing.
What condition are the DPFE hoses in?
I think it is time to take a step back and reevaluate the entire system. Here's the process I use at work to diagnose Ford EGR problems. Bare in mind that I'm looking at a scanner when I do this, so if something isn't clear it's probably because I've told you what I would be doing instead of what you should be doing.
1. Determine if the problem is on the "hot" or "cold" side. I define the hot side as anything that touches exhaust gases or the pressures they create. The cold side is everything else. To determine if the hot or the cold is causing the problem, apply vacuum to the EGR valve with the engine idling.
2. If the engine begins to run rough or dies you know that there is flow, but is it enough and is it being measured? You can check this with a DVOM connected between the center terminal of the DPFE connector and ground. You should be able to generate and measure at least 4 volts of flow. You will have to rev the engine a little to measure the max. flow; 1500 rpm should do it. If it passes this test, your problem is on the cold side. I'll cover cold side in a minute because a problem on the hot side is more likely.
3. If you didn't get 4 volts, how much did you get? The DPFE sensor typically either works or it doesn't. I have installed several that were bad out of the box, even Motorcraft, so your new one might not be doing the job. If the DPFE sensor voltage started going up, but then stopped before it got to 4V you more than likely have a restricted EGR passage somewhere. The passages in the intake are not easy to clean thoroughly. Even though you already did that, I would revisit them just to be sure. You can block the throttle open with something and put a mirror in the TB and actually see the ports. Some creative tweaking of a coat hanger will allow you to clean from both ends of the passage without removing the intake elbow. Just cleaning from the outside won't do the job since the passages have a 90 degree bend in them. After this, repeat step 2 and it will probably pass that test.
4. If the DPFE voltage didn't change at all, but the idle quality did, you need a new DPFE sensor or the hoses to it or both. You can replace the stock hoses with vacuum line for testing purposes, but they won't last long enough to be a permanent repair. I should also point out that it is possible that the harness connector at the DPFE sensor isn't making a good connection. It's rare, but it happens.
Cold side:
5. If all the tests above were passed, you have a problem on the cold side of the system. This includes the vacuum supply lines, EVR solenoid, wiring, and PCM. It sounds like the vacuum supply is good to the EVR. To test whether the PCM is requesting EGR flow or not, measure the voltage across the EVR terminals with a DVOM while driving. If it is commanding EGR flow and not getting it, the PCM will eventually quit trying as you have seen. If that's the case, there is something in the system that it really doesn't care for, and it's probably on the hot side.
6. If the PCM is not stopping EGR flow, the problem is either the EVR solenoid or the wiring to it.
There is a lot of gray area in diagnosing this code and there is also quite a bit of gut feeling involved. I think the above process will lead you to an answer, but it may or may not be an easy find.
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Freshman User
Joined: Nov 2004
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This is good info, Silver streak.
I'll answer inside your text, all that I can. (Bolded)
Thanks, I'm pretty good at wrenchin', but this thing has really got me bugged. It seems to be such a simple system, and I work on instrumentation for a loving. I'll update this thread tomorrow.
I'll answer inside your text, all that I can. (Bolded)
Originally Posted by Silver Streak
OK, I thought you meant you had good input to the EGR solenoid, not the valve. If it's to the valve you need to put a DVOM in parallel with the EVR solenoid and see if the PCM is commanding erratic vacuum, or if it's just happening. I'll do this on my commute to work tomorrow. You can also probe the middle wire on the DPFE sensor to see what kind of voltage you are getting while the EGR is operating. You should see between 2.5-3 volts cruising on the highway. I'll do this on my commute from work tomorrow.
When you said it abrubtly shuts off it got me to thinking. When the PCM detects a problem with the EGR system, it turns it off until you stop and it "resets" itself. I think that is what you are seeing.
What condition are the DPFE hoses in? Very good
I think it is time to take a step back and reevaluate the entire system. Here's the process I use at work to diagnose Ford EGR problems. Bare in mind that I'm looking at a scanner when I do this, so if something isn't clear it's probably because I've told you what I would be doing instead of what you should be doing.
1. Determine if the problem is on the "hot" or "cold" side. I define the hot side as anything that touches exhaust gases or the pressures they create. The cold side is everything else. To determine if the hot or the cold is causing the problem, apply vacuum to the EGR valve with the engine idling. Done. The engine stumbles, but does not die.
2. If the engine begins to run rough or dies you know that there is flow, but is it enough and is it being measured? You can check this with a DVOM connected between the center terminal of the DPFE connector and ground. You should be able to generate and measure at least 4 volts of flow. You will have to rev the engine a little to measure the max. flow; 1500 rpm should do it. If it passes this test, your problem is on the cold side. I'll cover cold side in a minute because a problem on the hot side is more likely. OK
3. If you didn't get 4 volts, how much did you get? The DPFE sensor typically either works or it doesn't. I have installed several that were bad out of the box, even Motorcraft, so your new one might not be doing the job. If the DPFE sensor voltage started going up, but then stopped before it got to 4V you more than likely have a restricted EGR passage somewhere. The passages in the intake are not easy to clean thoroughly. Even though you already did that, I would revisit them just to be sure. You can block the throttle open with something and put a mirror in the TB and actually see the ports. Some creative tweaking of a coat hanger will allow you to clean from both ends of the passage without removing the intake elbow. Just cleaning from the outside won't do the job since the passages have a 90 degree bend in them. After this, repeat step 2 and it will probably pass that test.
The ports were severely clogged and cleaned ~~45Kmiles ago. I will recheck to see if they are partially blocked again.
4. If the DPFE voltage didn't change at all, but the idle quality did, you need a new DPFE sensor or the hoses to it or both. You can replace the stock hoses with vacuum line for testing purposes, but they won't last long enough to be a permanent repair. I should also point out that it is possible that the harness connector at the DPFE sensor isn't making a good connection. It's rare, but it happens. I cleaned the connector tonight when I got home will look for results tomorrow.
Cold side:
5. If all the tests above were passed, you have a problem on the cold side of the system. This includes the vacuum supply lines, EVR solenoid, wiring, and PCM. It sounds like the vacuum supply is good to the EVR. To test whether the PCM is requesting EGR flow or not, measure the voltage across the EVR terminals with a DVOM while driving. If it is commanding EGR flow and not getting it, the PCM will eventually quit trying as you have seen. If that's the case, there is something in the system that it really doesn't care for, and it's probably on the hot side.
6. If the PCM is not stopping EGR flow, the problem is either the EVR solenoid or the wiring to it.
There is a lot of gray area in diagnosing this code and there is also quite a bit of gut feeling involved. I think the above process will lead you to an answer, but it may or may not be an easy find.
When you said it abrubtly shuts off it got me to thinking. When the PCM detects a problem with the EGR system, it turns it off until you stop and it "resets" itself. I think that is what you are seeing.
What condition are the DPFE hoses in? Very good
I think it is time to take a step back and reevaluate the entire system. Here's the process I use at work to diagnose Ford EGR problems. Bare in mind that I'm looking at a scanner when I do this, so if something isn't clear it's probably because I've told you what I would be doing instead of what you should be doing.
1. Determine if the problem is on the "hot" or "cold" side. I define the hot side as anything that touches exhaust gases or the pressures they create. The cold side is everything else. To determine if the hot or the cold is causing the problem, apply vacuum to the EGR valve with the engine idling. Done. The engine stumbles, but does not die.
2. If the engine begins to run rough or dies you know that there is flow, but is it enough and is it being measured? You can check this with a DVOM connected between the center terminal of the DPFE connector and ground. You should be able to generate and measure at least 4 volts of flow. You will have to rev the engine a little to measure the max. flow; 1500 rpm should do it. If it passes this test, your problem is on the cold side. I'll cover cold side in a minute because a problem on the hot side is more likely. OK
3. If you didn't get 4 volts, how much did you get? The DPFE sensor typically either works or it doesn't. I have installed several that were bad out of the box, even Motorcraft, so your new one might not be doing the job. If the DPFE sensor voltage started going up, but then stopped before it got to 4V you more than likely have a restricted EGR passage somewhere. The passages in the intake are not easy to clean thoroughly. Even though you already did that, I would revisit them just to be sure. You can block the throttle open with something and put a mirror in the TB and actually see the ports. Some creative tweaking of a coat hanger will allow you to clean from both ends of the passage without removing the intake elbow. Just cleaning from the outside won't do the job since the passages have a 90 degree bend in them. After this, repeat step 2 and it will probably pass that test.
The ports were severely clogged and cleaned ~~45Kmiles ago. I will recheck to see if they are partially blocked again.
4. If the DPFE voltage didn't change at all, but the idle quality did, you need a new DPFE sensor or the hoses to it or both. You can replace the stock hoses with vacuum line for testing purposes, but they won't last long enough to be a permanent repair. I should also point out that it is possible that the harness connector at the DPFE sensor isn't making a good connection. It's rare, but it happens. I cleaned the connector tonight when I got home will look for results tomorrow.
Cold side:
5. If all the tests above were passed, you have a problem on the cold side of the system. This includes the vacuum supply lines, EVR solenoid, wiring, and PCM. It sounds like the vacuum supply is good to the EVR. To test whether the PCM is requesting EGR flow or not, measure the voltage across the EVR terminals with a DVOM while driving. If it is commanding EGR flow and not getting it, the PCM will eventually quit trying as you have seen. If that's the case, there is something in the system that it really doesn't care for, and it's probably on the hot side.
6. If the PCM is not stopping EGR flow, the problem is either the EVR solenoid or the wiring to it.
There is a lot of gray area in diagnosing this code and there is also quite a bit of gut feeling involved. I think the above process will lead you to an answer, but it may or may not be an easy find.
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Postmaster
Joined: May 2002
Posts: 3,241
Likes: 3
From: Broken Arrow, OK
It is a simple system, but there's lots of little boxes full of voodoo magic involved so diagnosis is a little sketchy the first few times you do through it.
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Well, here are the results of my latest test drive.
Back probed top wire on the DPFE and ground with DVOM while driving. (I made a temporary harness to the cab.)
At idle 1.05 volts.
Under pretty hard acceleration ~~ half to two thirds throttle. 1.29 volts.
Cruise 55 to 65 mph, 1.17 to 1.2 volts and never saw more than 5.5 inches vacuum.
Now, if I'm guessing right. the problem appears to be on the "hot" side.
Tomorrow, I'll double check the throttle body ports and I might put my old DPFE back on to see if it has exactly the same voltage values.
Crossing fingers here in Atlanta.
Back probed top wire on the DPFE and ground with DVOM while driving. (I made a temporary harness to the cab.)
At idle 1.05 volts.
Under pretty hard acceleration ~~ half to two thirds throttle. 1.29 volts.
Cruise 55 to 65 mph, 1.17 to 1.2 volts and never saw more than 5.5 inches vacuum.
Now, if I'm guessing right. the problem appears to be on the "hot" side.
Tomorrow, I'll double check the throttle body ports and I might put my old DPFE back on to see if it has exactly the same voltage values.
Crossing fingers here in Atlanta.
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Freshman User
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I pulled the throttle body off the engine, and it seems that only 42k miles is more than enough to almost complettely clog the EGR ports.
I cleaned them thoroughly and reassembled. The voltages are much improved wth about 2.7 volts at cruise. Tomorrow's commute to work will tell the tale.
Thanks in advance for the good troubleshooting advice. It really is a simple subsystem, just tricky. I was trying to make the problem more complex than it really was, and started way too early throwing money at it intead of getting dirty for free.
I took a few pictures of the disassembled throttle body if anyone would like to get them.
<!-- / message -->
I cleaned them thoroughly and reassembled. The voltages are much improved wth about 2.7 volts at cruise. Tomorrow's commute to work will tell the tale.
Thanks in advance for the good troubleshooting advice. It really is a simple subsystem, just tricky. I was trying to make the problem more complex than it really was, and started way too early throwing money at it intead of getting dirty for free.
I took a few pictures of the disassembled throttle body if anyone would like to get them.
<!-- / message -->
