Fix code P0401 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.
© 2012 Rick Muscoplat
Posted on by Rick Muscoplat