P0400 EGR FLOW MALFUNCTION is a blockage code, not a component failure. What the computer is letting you know is that something is preventing the EGR valve from opening and closing. A sensor mounted just above or near the EGR valve checks pressure to veryify that the EGR valve is indeed doing it's job. When the EGR fails to do it's job, that's when P0400 code surfaces. The typical cause of this code is cracked vacuum hoses or clogged hoses and or components with nasty carbon buildup inside of them. Each and every vacuum line to the EGR system needs to be checked! Carbon clogging also occurs inside the throttle body where the maze of vacuum lines originate. The task of unclogging those holes on the throttle body can become tideous, but needs to be performed in order to open up the vacuum flow. Rarely does a component failue throw a P0400 code, but when it does, it's one of three things. 1) EGR valve diaphragm is cracked and leaking vacuum, 2) The EGR plenumn sensor has failed 3)The amount of voltage getting to the sensor is not enough with a certain window, and will throw a P0400 code.
Monday, May 19th, 2008 AT 4:04 PM