# PO401 check engine light code



## soonerdean (Oct 21, 2016)

Hi everyone, 
The dreaded check engine light came on last week. I was finally able to put a code reader on the car and the "PO401" code came back. This is an insufficient EGR air flow or something like that. Not really sure what that means. I changed the EGR valve but the code returned. I"m hoping someone can tell me how to resolve this issue. THanks in advance for any help you can provide.


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## cngarch (Sep 5, 2018)

Check for vacuum leaks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Get yourself a multi meter and get on utube and type in checking knock sensor on your car. they do go bad but with small hands an a lot of cuts (the gaskets are stainless steel and will cut you) they can be replaced without taking the intake manifold off the engine($600.00).

Otherwise have the fuel pressure checked. On these older cars the fuel pump can trigger the knock sensor code. I have a 1996 infinity with 268000 miles and it runs fine but does have problems with vacuum leaks which can cause a lot of problems. misfiling, poor gas mileage, pcv valve codes. Diagnosis in 1996 was in it infancy and OBT2 codes were also. The problem is often far from what it says.

I have also had to take the intake manifold off to replace the valve cover gasket. A common problem. I have had the transmission fluid replaced every 75000 miles. (synthetic)


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