P0402 Exhaust Gas Recirculation Flow Excessive Detected
Hello, I have a F150 4.6 liter with 85000 miles on it and I keep getting the Code P0402 Exhaust Gas Recirculation Flow Excessive Detected. I have changed the DPFE sensor and the EGR Valve and the EGR Vacuum Solenoid. Basically everything in the chain of the Vacuum lines. I cant seem to get this code to go away and I think it is affecting my gas milage to. Any help on where to go next would be appreciated. Thanks
Here is an example of knowing what the 402 test is doing.
Basicly the PCM looks at the DPFE with the EGR closed such that no flow is supposed to occurr.
How it detects this is the DPFE sees the same exhaust pressure on both sides of the calibrated orfice indicating there is no flow or 'pressure drop' accross the orfice.
If there is a leak in the pipeing off the exhaust manifold, any hoses are leaking that connect the DPFE to the test tubes or a leaking EGR, the DPFE will not signal the pressure is the same on both it's ports. (sort of like a 401 test when it is not the expected results of the test)
This test is done at cold startup-drive-away to use the extra exhaust pressure of the motor as it is increasing in rpm.
Inspect closely the metal tube at the exhaust for cracks, rust holes as well as the DPFE hoses and small connecting tubes for a problem.
Test the operation of the EGR to be sure it is seating closed.
Test that the vacuum control that operates the EGR is allowing the EGR to close because it is a 3 port device that must let air into the EGR once it has been opened so it will close again and not hang up.