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The service engine soon light is on, it didnt start coming on til i changed the power steering pump and hoe the code it gets is po401 egr system, i wonder if i forgot to attach a hose?
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diagnostic aids:
a vacuum restriction to the map sensor--a skewed map sensor reading can cause the PCM to read an incorrect MAP change during the EGR flow test
an engine that is running poorly due to mechanical condition such as worn piston rings, ect. can cause low engine vacuum thus EGR flow test will fail
excessif backpressure of the exhaust system can cause P0401
exhaust system leak can cause an insufficient amount of EGR flow
a restriction in the intake manifold such as carbon deposit and casting flash.
someone removed the egr. or someone replaced the engine with a non egr engine. if the engine was changed you ether need to put an egr system on it or change the computer with one made for an egr exempt engine.
Well, the po401 is saying is that the egr valve has restricted flow. After changing the egr and the tube, something else is causing the restriction. a more thorough diagnosis is recommended. The po420 code sounds like a possible catalyst failure or an o2 sensor failure.
I believe this code is insufficient EGR flow. On this engine, the passages to the EGR valve often become carboned up and cause this code. Remove the EGR valve and inspect the passages to see if they need to be cleaned.
Does the egr vavle open ? You will need to use a scanner to test the dpfe voltage when the egr valve is energized you should read around 3.5 4.00 volts. Also you could remove the vacume line from the egr valve and with the engine running you should see around 100 rpm drop in engine rpm at least this would indicate the egr valve is capable of flowing egr gases through the system to the cylinders.
PO401 code means that:
The PCM has determined that there is insufficient flow in the exhaust gas recirculation system.
Definition: EGR system fault (Exhaust Gas Recirculation)
Probable Causes:
a. Blocked passage on EGR system
b. Failed EGR Valve
c. EGR solenoid faulty
d. Failed EGR pressure sensor where applicable
e. Failed EGR position sensor where applicable
the egr valve for your expedition is about $ 60 to 70 dollars. it wil get better fuel mileage and run better also . it regulates the exaust back into the intake for optimum combustion.
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