P0401 - Tried Everything.. still getting codes.

[JMSports]

I have a 96 Sport with a 4.0 and 241,000 miles. I had a CEL P0401 for EGR insufficient flow, as well as P0420 Cat Converter Efficiency below threshold.

I replaced the valve itself (which now I realize I didnt need to do), and the code came back. I blew out the lines going to the DPFE and a bunch of small **** came out. Code still came back. I replaced the original DPFE with an updated plastic one. Code still came back. I took the valve off to check for vacuum at the intake port of the system and it damn near sucked my finger in so theres plenty of vacuum. Code still came back. All that left to check is the Solenoid. With the engine at idle, that little green vacuum tube that goes to the top of the EGR is pulling vacuum. Im not sure if this vehicle has a pulse width modulation system or not, but Idk if I should just replace the Solenoid. everything else is replaced.

Any Ideas? (btw im not getting the 420 code for the cats, just the EGR code keeps coming back)

 

[jremington59]

When you say an updated DPFE do you mean a new one?

Before you went and did all of this did you check to see if the tube was plugged with carbon?

 

[JMSports]

Updated as in the originals were metal and often had issues with heat absorption, and the newer designs are plastic. I bought a new one.

 

[JMSports]

When you say an updated DPFE do you mean a new one?

Before you went and did all of this did you check to see if the tube was plugged with carbon?

The tube is free and clear.

 

[jremington59]

I'm talking about the EGR tube. Make sure it's not plugged at the base next to the manifold.

If you've changed everything except the sensor, and everything is OK, including no leaks in vacuum lines, then it has to be that last sensor.

Just for the heck of it, take a piece of vac line and fasten it to the EGR valve. Start the engine and with your mouth suck in lightly on the other end of the line and make sure the engine stumbles.

 

[1998Explodasport]

I had the same problem one of my vehicles and it ended up being a bad wire that ran to the DPFE sensor from the computer.

 

[JMSports]

I'm talking about the EGR tube. Make sure it's not plugged at the base next to the manifold.

If you've changed everything except the sensor, and everything is OK, including no leaks in vacuum lines, then it has to be that last sensor.

Just for the heck of it, take a piece of vac line and fasten it to the EGR valve. Start the engine and with your mouth suck in lightly on the other end of the line and make sure the engine stumbles.

Shouldnt the EGR not be getting vacuum at idle? Only during accel?

 

[jremington59]

Exactly. That's why if it stumbles you'll know the EGR is good. It wouldn't be the first time a new part was faulty.

Is there a solonoid mounted to the top of your EGR valve? I went through this same thing when I bought mine. It ended up being the gasket between the EGr and the solonoid. But I don't think yours has it with the DPFE.

 

[JMSports]

Exactly. That's why if it stumbles you'll know the EGR is good. It wouldn't be the first time a new part was faulty.

Is there a solonoid mounted to the top of your EGR valve? I went through this same thing when I bought mine. It ended up being the gasket between the EGr and the solonoid. But I don't think yours has it with the DPFE.

Nope, the solenoid is mounted next to the DPFE on the side of the motor.

 

[jremington59]

For some reason I thought yours was the 5.0. There's so many of these egr threads I can't keep them straight. Did you end up trying the new sensor?

 

[JMSports]

What new sensor are you talking about? I replaced the DPFE already to no avail.

 

[jremington59]

In your first post you asked if you should just replace the solonoid.

If you've replaced everything new, and you're sure there are no vacuum leaks you could have low vacuum.

Did you ever put some vacuum to the egr and see if the engine stumbles? I suppose it could be possible the new EGR is faulty.

 

[2000StreetRod]

What results in P0401?

The PCM provides a variable duty cycle rectangular waveform to the EGR vacuum regulator (EVR). The EVR (which is merely a solenoid controlled vacuum valve) modulates the vacuum according to the electrical waveform. The EVR vacuum line controls the opening and closing of the EGR valve. The DPFE sensor measures the difference in pressure before and after an orifice in the EGR tube. It generates a voltage proportional to the differential pressure and sends it to the PCM.

One of the tests the PCM performs is to attempt to open the EGR valve. It can only determine if the valve is open by the voltage generated by the DPFE sensor. If the PCM reads a too low voltage when the EGR valve should be fully open it sets DTC P0401.

You have replaced the EGR valve so it should be responding properly. You have replaced the DPFE sensor so it should be measuring pressure correctly and generating the corresponding voltage. Since the PCM is not generating P1400 or P1401 I would assume that there is a good electrical connection between the DPFE sensor and the PCM.

In my opinion the only remaining possible trouble sources listed in order of most likely to least likely are:

1. Clogged EGR tube, clogged EGR ports, or clogged or leaking DPFE port pipes or hoses.

2. Defective EVR, leaking vacuum line from EVR to EGR valve, or leaking vacuum hose from intake manifold to EVR.

3. Poor electrical connection from PCM to EVR.

There is a test for the EVR in post #4 of my thread:EGR System O&T

 

[JMSports]

In your first post you asked if you should just replace the solonoid.

If you've replaced everything new, and you're sure there are no vacuum leaks you could have low vacuum.

Did you ever put some vacuum to the egr and see if the engine stumbles? I suppose it could be possible the new EGR is faulty.

No I didnt get to replace it yet.