Where are the fuse boxes located a 2004 mercury monterey?

SOURCE: how to get to the rear spark plugs in a 2004

under the vehicle and its still no easy chore

SOURCE: 2004 Mercury Monterey 70k CEL code PO401

po401 egr flow insufficient vaulve could be stuck or disconected

SOURCE: Keyless Entry keypad code for Mercury Monterey?

Actually, if you look under the dash board, near the steering column, there should be a box that has the code printed on it.

SOURCE: where is egr valve on 2004 mercury monterey mini

You can get the EGR Valve for $80.00 OEM Motorcraft
Part, on the internet and install your self

The code better be for an EGR Valve issue or
be having issues going up hill under a load or
that isn't your problem

SOURCE: What's your problem? my 2004 mercury monterey

PO 300 is multiple misfires detected
PO 301, 304, 305, 306 are misfires in cylinders 1,4,5,&6
PO 053 is HO2S Bank 1 Sensor 1 Heater Resistance
PO 106 is MAP/BARO CKT Range / Perf
PO 316 is Misfire detected 1st 1000 Revs.

On a misfire, I usually push towards the spark plugs, plug wires, and coil packs / distributor coil.
You have PO 106 and PO 053 that need to be inquired about at nearest AutoZone.
They can give you an idea as to what is the problem on these.

Did a MAP sensor **** out and cause all the misfires ?
Did a misfire cause the MAP sensor error?
You see what I'm saying ?...Something caused all the misfires...thinking MAP...but not that familiar with the function of the MAP.

Hope this helps...