Does anyone know what a P0401 could be caused by?

 

Looking at mazdas dtc chart there is not a P0401 but there is a P0403 which is EGR valve (stepper motor) circuit problem.

 

Is there a code thrown for engine knock?

 

You would think so but there is not, the closest it would get is a misfire code.

 

A code P0401 most likely means one or more of the following has happened:

* The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
* There is a blockage in the EGR (tube), most likely carbon buildup
* The EGR valve is faulty
* The EGR valve may not be opening due to a lack of vaccuum

 

replace the egr ~$65 and hope for the best?

 

I've only got 40k miles on it and I have 100k miles of warranty. So I maybe should be ok there. I just have to wait for it to pop up again now that I've cleared it.

 

So they said it is the EGR valve. They are replacing it and all should be well again. I asked what the price would be normally and it is $99 for the part and 1.5 hours in labor. So an EGR valve replacement would normally cost around $330 at the dealer with a bit of a discount for the insurance company. I'm guessing it would be around $350 or so for the average person.

I also had them inspect the cooling system. I regularly get a film on the inside of the windshield and my coolant level drops some. I thought maybe I had a heater core issue. They said the system all looks ok. Apparently, the dash has a chemical in it that off gasses and causes the film. It is a TSB from what she said. And the coolant level dropping is normal. They (Mazda engines) seem to do this and you just top them off.

Yay, now I can put my tune back on the car!

 

i was gonna get that hypertech thing, but then i thought 350+ for 7-10hp....NAH, id buy a used one for 150 tops

 

Yeah, if I had to buy it at full price I'm not sure either. Another reason why I haven't gotten a CAI.