2000 Ford Expedition P0401 doesn’t necessarily mean the EGR is bad

Don’t replace the EGR (Exhaust Gas Recirculation) valve just yet if you have a P0401 code on a 4.6 liter engine like the one in this Expedition. The diagnostic code definition states “Low flow from E.G.R.” Low flow doesn’t mean definitively that the EGR is bad. Low EGR flow can be a problem in any Ford, Mercury, Lincoln, Mazda and many other car’s for that matter. On a lot of Ford vehicles this code will mean there is a faulty Differential or Delta Pressure Feedback (DPFE) sensor. This was such a common problem there was an extended warranty coverage on them for awhile. Not many people knew about Ford covering these on some models for an extended period of time. At the shop I worked at, an extended warranty company first alerted us to this when they declined an extended warranty claim because Ford would replace it under warranty.

What is a DPFE and what does it do?

The DPFE helps the vehicle’s computer to insure that the EGR (Exhaust Gas Recirculation) system is working properly. The sensor monitors the exhaust pressure in the exhaust, usually from a passage in the vehicle’s intake. The sensor sends a reading to the vehicle’s computer. If the expected changes in pressure are not seen by the PCM (Power Train Control Module) the CEL (Check Engine Light) will be turned on. Most of the time performance issues aren’t noticeable. Sometimes pinging upon acceleration can be detected if the DPFE is not working properly. It is usually located near the EGR, in fact some late model Ford’s have the DPFE built right into the EGR. The sensor is prone to failure mainly because of the harsh exhaust it is exposed to. Between carbon build up and corrosion, a bad DPFE is a common problem. On the 2000 Ford Expedition, the original DPFE was aluminum… it doesn’t rust! The problem is that aluminum does corrode. The replacement DPFE is made of plastic, which is an improved design but failures of these are still fairly common.

With throttle body removed and mirror in place the passages can be seen

The two dark spots are two badly restricted EGR passages

EGR Passages

The passages on the Expedition in the picture above are shown with the throttle removed. They are obviously restricted, completely blocked off with carbon build up. The passages go down, then to the right where they meet with the EGR. With the EGR removed, the passages can be cleaned out with fuel injection spray cleaner, a spare coat hanger and a thin bottle brush from the kitchen. Compressed air helps blow through the gunk and clear the passages, allowing the EGR, DPFE and PCM to work together.

• Vacuum can be applied to an EGR with a hand vacuum pump, while it’s running to see if the idle drops. Sometimes the idle can drop some but the passages may still be partially clogged.
• When replacing a DPFE sensor, if there are rubber hoses, blow through them with compressed air to clean out any loose debris.
• Replace DPFE hoses that have excessive deterioration. Regular hoses won’t work, it takes special DPFE sensor hoses to withstand the high temperatures.
• Try cleaning the EGR passages first to attempt to save money. Replace the DPFE sensor if the diagnostic code returns.
• Don’t buy a used one, this is such a common problem chances are not good to find a good one in a salvage yard.
• The diaphragm in the EGR can leak but it’s not as common as the above mentioned problems.

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