CEL P0401

[Captain Mazda]

CEL suddenly came on while I was on the freeway and this is what my BlueDriver reported:

P0401 CODE DEFINITION:
• EGR "A" Flow Insufficient Detected
4 POSSIBLE CAUSES
• EGR has failed
• EGR valve connector is damaged (check pins for damage, and for moisture)
• MAP sensor has failed
• PCM has failed

FREQUENTLY REPORTED FIXES:
• Replaced Exhaust Gas Recirculation (EGR) Valve
OTHER REPORTED FIXES:
• Cleaned Exhaust Gas Recirculation (EGR) Passage(s)
• Replaced Mass Air Flow (MAF) Sensor


Seems like a fairly easy fix once you figure out what's causing it but my dealership won't do this kind of work on weekends. Can anyone recommend a reputable shop that can diagnose this on a Saturday?

[Flagrum_3]

First thing I'd try is cleaning and inspecting the EGR and MAF connectors. Also check that the female connectors are tight before anything else. Least scenario is that any sensors are bad in my opinion.


_3

[G ~ MINI]

I did replace the MAF last year. CEL would come on. Reset it ... Then 2 months later come on again ...
I did check and clean connectors and clean air filter and box .... CEL came back on a couple of months later..
Not sure if youre having same scenario now
Has not come on since replacing part myself.

[Flagrum_3]

I did replace the MAF last year. CEL would come on. Reset it ... Then 2 months later come on again ...
I did check and clean connectors and clean air filter and box .... CEL came back on a couple of months later..
Not sure if youre having same scenario now
Has not come on since replacing part myself.

I had a similar issue, was getting the P2229 code (Barometric Pressure Circuit High). Would clear it and it would come back. Cleaned the MAF, tightened the female connector side on the harness with no result. Turns out my cold air intake was loose due to a broken mounting bolt causing the intake to jostle around. Unfortunately it loosened or broke a wire in the connector itself. Had to solder in a new connector which a friend cut off another harness from a scrap Mazda3 and put a new bolt on the CAI...

Everything is back too 100% now.


_3

[Captain Mazda]

Filled up last night after my game and the CEL was gone 0_o

Will keep an eye on it for now, but does it indicate a bigger issue? Or maybe a faulty MAF sensor?

[G ~ MINI]

Check the link ... https://www.fiix.io/car-advice/articles/signs-of-a-failing-mass-air-flow-sensor

Never knew you can clean a MAF....and other reasons that trigger CEL

[Captain Mazda]

I would notice even the slightest change in fuel economy because I track every fill-up. Also the engine hasn't been acting up at all.

[G ~ MINI]

I would notice even the slightest change in fuel economy because I track every fill-up. Also the engine hasn't been acting up at all.

Its hard to say if it were just a dirty MAF or something minor within the sensor and triggering a CEL
Not sure if ECU would run a limp home mode or just run a preloaded set of parameters
But ....Im sure if it were something major and CEL MAF is triggered you would see a drop in fuel economy.

MY CEL P0401 would always trigger with the weather was wet and then go away....until next wet
and then would not reset (i knew then it was time to replace)

[Captain Mazda]

Yeah I've never had this issue before and the engine has been running normally. I'm gonna try to get a service visit in just to get things looked at.