my engine light came on with a code p0401 it is bad?

not true, what you need to do is to read the codes in your computer with a scan computer and replease the sensor that is not working properly

http://www.obd-codes.com/p0401 P0401 is Insufficient EGR Flow, it may be true your engine needs a tune up but this alone is not going to attend to the true cause of the Check Engine Light being on.

just my take on this; have a 04 monterey van (best road beast ive ever had....); if you engine light is on solid...return fuel sensor and fuel filter need to bee replaced. if your engine light is blinking....whoe to you...catylitic converter. 03/09/12 spent 800 on new gas limiter/sensor (left rear of engine block) new drive belt and front end align with two new tires; front wheel drive love it; 4.2 litre side six (i've blown off mustangs from time to time). veriy comfortable leather fully adj. seats and all good stuff. cd/am/fm/engine comp totally clean etc. no brag, just fact. took a year or so to get this machine trustworthy. i'd take it anywhere/anytime.