One problem related to gas recirculation valve (egr valve) has been reported for the 2004 Ford Explorer. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Ford Explorer based on all problems reported for the 2004 Explorer.
I purchased a 2004 Ford Explorer in July 0f 2011, and traded in my 2001 Oldsmobile of 5 years. I also purchased the 12 month 12,000 mile warranty. Before driving it off the lot I had the dealer fix the abs system because the light was on. There is a crack going down the back of the trunk but nothing else was wrong at the time so I left the crack alone. In April of 2012 I took it to the dealership for a belt, check trans, shocks, ball joints, and a ticking in the heater when knob was turned to heat (not cool). I told him to just fix what was on the warranty and also give it a oil change. He informed me that the trans was fine. After getting the car back my heat went out and I was told by a mechanic buddy that my brakes, rotters, emergency brake pads and the back tires were shot. So I had him replaced them because this was also not covered on warranty. Just last week my rpm started jumping with miles over 65. (no lights were on at the time)so I took it to 6 different places getting estimates on what could be wrong. All shops said the same thing. "start with fuel filter, oil filters and oil change". The day after I paid for all this the service engine light came on. (egr valve code) the man at auto zone told me to take it off and clean it with spray and let it dry before replacing. I took it to a shop and had them do this. The same day I picked up the car my service engine light came on again, o/d light and the car was driving like I was hauling a bus and jumping. I took it back the next day and he replaced the egr valve new since the same code was showing up. Later that day after getting it back the car started doing the same thing after driving for 5 miles this was Friday 9/21/12.