P0401 on Ford Vehicles
If you haven’t’ already done so, read the full explanation of the DPFE system posted here. This is a very common code of Ford vehicles and can drive people absolutely crazy. Don’t get sucked into throwing parts at this problem. It’s really a fairly simple system.
The computer wants to know if the EGR valve is recirculating the amount of exhaust gas that it instructed it to. In order to check that, the DPFE checks for a pressure change above and below a port. It reports the change to the PCM as a change in voltage. No change or not enough change can mean a bad DPFE (and there are LOTS of those), a bad EGR valve,(not quite as common), or passages that are filled with carbon buildup from the flow of exhaust gas (very common.)
So here’s how to troubleshoot the system.
1) Start by checking DPFE voltage with the key on and engine OFF. That’s base voltage. Unplug the electrical connector and check the brown/white wire. It should read 5 volts.
2) Plug in the connector and backprobe the Brown/Light Green wire. It should be .45-.60 volts (on the older metal-cased sensors). If your DPFE has a plastic case, look for .9-1.1 volts. If you don’t see those voltages, replace the DPFE, it’s bad.
3) Start the engine and check voltage on the Brown/Light Green wire again. IT SHOULD BE THE SAME as when the engine is off. If it isn’t, the EGR valve is leaking and allowing exhaust gas to flow at idle. That’s a no-no. Clean or replace the EGR valve.
4) Apply a vacuum (hand held pump) to the EGR. Voltage should rise, depending on how much vacuum you apply. The higher the vaccum, the higher the voltage. Plus, the engine should run rough and die. If you don’t see a higher voltage, either the EGR isn’t opening (which
you can check by removing it and applying vacuum), or the passages are clogged.
So, BEFORE YOU RUN OUT AND BUY A NEW EGR VALVE, CLEAN All the passages in the throttle body, intake manifold, and egr tube. Then repeat test #4 to see if you get a rough running engine. If the engine runs rough but you still don’t see higher voltage, then you can replace the DPFE.
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© 2007 Rick Muscoplat
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I have a ford ranger with a last resort oil drain plug recently installed. Is there a way or place that can tap out the plug threads to fit a new plug or do I need a new oil pan?
Re-tapping the nut inside the pan rarely works very long. Too much metal damage. Get a new pan.
I’m getting the p0401 error and have replaced the sensor, solenoid and valve. The hoses look fine, although I don’t have the tools to test them. The SES light keeps coming on. I also sprayed carb cleaner down the valve tube connected to the exhaust and blew it out with air. I removed the throttle body and cleaned out the intake hole. It’s a 24v dohc sable. SES light is back on. Any ideas? Thanks Rick! I’ve learned a ton already from your website reading up on this error. Dale
If you’ve done all that, then chances are the passages are clogged in the intake manifold. Yeah, I know. But that’s the only thing left that can restrict the flow and apparently it’s getting more and more common as these engines age. Don’t forget to write a letter to Ford thanking them for the great design.
replaced fuel pump ia gas tank but when i pulled down a plug on the right side top of tank broke off ford dont make new ones and all the repair shop wont sell me one just want to fix at there shop what the plug for and how can i get new one
Are you talking about an electrical plug? If so, the part you’re looking for is called a pigtail. Start at a NAPA store. If they can find one, call a junkyard. Splice it in with a soldering gun and heat shrinkable tubing.
But if you’re talking about an emissions tube, the only place you’ll find that is at a junkyard.