6th Gen ('00-'05): Check Engine Light Code P0401
#1
07-28-2019, 10:41 AM
Check Engine Light Code P0401
About two weeks ago my check engine light came on, the auto store said my egr valve was bad. I change that then had the code cleared, after about 100 miles of driving the light came back on. My mechanic ran a diagnostic and told me the MAP sensor was bad. I replaced the sensor and the PCV value at the same time. Drove about 30 miles yesterday, check engine light came back on. Took it back to the auto part store for a code read and the code they gave me was P0401. Any information on how to fix/clear the code would be appreciated.
#2
08-03-2019, 05:09 PM
When the EGR valve was replaced, were the ports/ EGR tube on the manifold base cleaned? There can be carbon build up when the EGR starts to go bad/get clogged and the new valve only restores partial flow.
The only simple thing is to disconnect and reconnect the harness to it to make sure the connection is good.
In simple terms, the EGR opens and directs exhaust flow into the intake through the EGR tube, which increases the pressure in the intake that is picked up by the MAP sensor and the PCM (powertrain control module) reads the sensor and adjusts open/close based on programmed pressure requirements. If the egr flow is clogged, not enough pressure. If the MAP is dirty/bad, bad pressure reading. If the connection is bad, no proper open/close timing (same if the EGR was bad and not opening).
Also, what tier of gas are you using? Have you used fuel system cleaners? Have you changed your air filter within recommended mileage? A poorly running engine can produce more carbon build up. None of these should instantaneously correct the problem but are cheap and easy.
Also, you can get a bluetooth OBD reader module pretty cheap and download a free app to a smartphone that can read pending codes and tell you what the codes are and clear them. Some times, the PCM will set a code and then determine there isn't a problem after all. I had the P0401 code come on/off over a few hundred miles last fall/winter and then clear itself before I got to the point of actually taking off and cleaning the EGR valve. (I threatened it by buying a new gasket and it shaped up). :-) I have a friend who swears it is the gas formulation. I alternate between QT and Shell mostly now but I'm not saying other brands/(non) were the issue since we switch to a summer formulation here.
The only simple thing is to disconnect and reconnect the harness to it to make sure the connection is good.
In simple terms, the EGR opens and directs exhaust flow into the intake through the EGR tube, which increases the pressure in the intake that is picked up by the MAP sensor and the PCM (powertrain control module) reads the sensor and adjusts open/close based on programmed pressure requirements. If the egr flow is clogged, not enough pressure. If the MAP is dirty/bad, bad pressure reading. If the connection is bad, no proper open/close timing (same if the EGR was bad and not opening).
Also, what tier of gas are you using? Have you used fuel system cleaners? Have you changed your air filter within recommended mileage? A poorly running engine can produce more carbon build up. None of these should instantaneously correct the problem but are cheap and easy.
Also, you can get a bluetooth OBD reader module pretty cheap and download a free app to a smartphone that can read pending codes and tell you what the codes are and clear them. Some times, the PCM will set a code and then determine there isn't a problem after all. I had the P0401 code come on/off over a few hundred miles last fall/winter and then clear itself before I got to the point of actually taking off and cleaning the EGR valve. (I threatened it by buying a new gasket and it shaped up). :-) I have a friend who swears it is the gas formulation. I alternate between QT and Shell mostly now but I'm not saying other brands/(non) were the issue since we switch to a summer formulation here.
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