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Mountaineer EGR problem

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I have a 2002 Mercury Mountaineer 6 cyclinder engine and the Service Engine Soon light came on about a month and half ago. I took the car to AutoZone and had the OBD codes read. The code reader said 0401 which indicates a problem with the EGR system.

I replaced the EGR Valve and the problem did not go away. I then replaced the Vaccuum Regulator/Solenoid and the problem did not go away. I then replaced the Differential Pressure Sensor and the SES light went out but came back on after 4 days.

I am at a loss now. What else could I possible check or replace now? How can I tell if there is a leak in the vaccuum hoses? Could there be some kind of blockage in the pipes that circulate exhaust gases to and from the EGR valve?
Submitted: 10 years ago.
Category: Car
Expert:  JONATHAN replied 10 years ago.
Have you confirmed that it was p0401 that returned?
Customer: replied 10 years ago.
Reply to JONATHAN's Post: I had my wife drive the Mountaineer back to AutoZone to get the OBDII code read again. She said the code that was read this time was P0402 - EGR Flow Excessive.

From what I've read online people usually say this indicates a bad DPFE (Differential Pressure Feedback EGR) sensor. But I just replaced this part with a new one from AutoZone. I also replaced the EGR's Vacuum Regulator (solenoid) with a new part, too.

One thing that I forgot to mention earlier. When I was replacing the EGR Valve with a new one about a month ago, I noticed a small round piece of foil that seemed to be attached to either the old EGR valve or the EGR orifice tube itself. I don't know what this could have been but I remember thinking it may have clogged the EGR valve somehow (but then again it seemed attached/glued on, so I don't know). The foil didn't look perforated so I don't think it was a screen. It's hard to remember since it was a month ago...

Is there a way that I check the voltage on the DPFE? If so what voltages should I look for?

What's the likelyhood that the new parts are bad?
Expert:  JONATHAN replied 10 years ago.
Question is if the dpfe sensor is a revised sensor...Ford/Mecury had a lot of problems with these sensors and they have been redesigned...they are a 5 volt reference sensor...three wires...5volt reference...a sensor ground and a sensor output wire...on the sensor output wire ....on the sensor output wire you should see about .45 volts key on engine will rise depending on the amount of pressure up to about 4.5 volts...the foil was the egr gasket that was used on the original valve....if you have the old sensor i would call a mecury/ford dealer and see if the part has been revised......
Customer: replied 10 years ago.
Reply to JONATHAN's Post: Jonathan,

Just a few more questions...

How do I attach a voltmeter to the sensor? Seems like if I unplug the connector then it won't get 5 volts or ground any more.

Unfortunately, I threw my old sensor away. Do you think AutoZone gave me a faulty part or a DPFE for a different vehicle (I kinda doubt it because it looked almost identical)? Maybe they'll exchange the part for me since I just bought it from them last weekend.
Expert:  JONATHAN replied 10 years ago.
it needs to be backprobed to measure the voltage...i usually use a thin paper clip and carefully slide it up the insulation until it makes contact with the contact terminal inside the connector...the five volt reference is on one side of the connector and the signal output is on the opposite end....its quite possible its a faulty part....were the egr valves identical?
Customer: replied 10 years ago.
Reply to JONATHAN's Post: The EGR valves looked identical in size and shape to me. I don't know if they were manufactured by the same company or not, though.
Expert:  JONATHAN replied 10 years ago.
that could be a problem as well...if its not a ford egr valve and it has a different diameter pintle then it could be causing this fault as well....sometimes ford does sell their parts to aftermarket there anyway you could check for ford stamping or part numbers on them?
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