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Old 02-08-2014
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Engine Light Back On..DPFE Sensor


A couple of weeks ago my engine light came on and went and had it checked and the code said it was the DPFE EGR sensor, I changed it and got a new one, well afterwards I drove over 200 miles with it and the light never shut off, so I went back to the place Auto Zone it was still reading the same code.....

So the guy just erased the code and the light stayed off for 2 weeks, but now it's back on......

I know there's always a chance I got a defective sensor, but really don't feel like buying another, is there something else that can be triggering the light to come on and make this code come back..?

Thanks For Any Info
Error code P0401
2000 Ranger 3.0 4x4
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Old 02-08-2014
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p0401 doesn't mean DPFE sensors is bad

p0401 means EGR flow into intake is not correct.

Ford p0401, Exhaust Gas Recirculation Flow Insufficient Detected

EGR(exhaust gas recirculation) system has 3 main parts
DPFE sensor
Vacuum lines
EGR Valve/tube

With a 2000(14 years old) you could have carbon build up in the tube and valve so exhaust gas flow is limited.
It is free to have a look.

Vacuum lines are also easy to check, remove and inspect for hardness and/or cracks.

To check if EGR valve is working connect a vacuum line to top connection on EGR Valve.
Start engine
Suck on that vacuum line, this will open the EGR valve and engine should start idling very rough and if opened long enough engine should die.

If everything checks out, then test the DPFE sensor.

Most sensors and controls can be tested with OHM/Volt meter.

Just for future reference, sensors and controls are often replaced but rarely fail.
Often the removing of the connector to install the new sensor or control fixed the problem, i.e. a bad connection, so new sensor was not needed.

The Check Engine Light(CEL) coming on usually means a sensor IS working, the computer can only "see" a problem if the sensor is working and "tells" the computer of something being out of normal range.
Auto parts stores offer "free" OBD reading because it makes them money, there are a few codes that will tell you a sensor is acting up, but for the most part OBD code means a sensor is working and reporting a problem with the system it monitors, so "don't shoot the messenger"
An engine running poorly with no CEL can mean a sensor or control has failed, not always but more likely.

And as you found out you need to reset computer after doing any engine work or CEL will often stay on.
You just need to disconnect negative battery terminal for 5 minutes to reset computer, so while doing any engine work disconnect battery, not only for safety but to reset computer.

Last edited by RonD; 02-08-2014 at 01:07 PM.
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