I have read carefully what you have written and I had the same failure with my 2017 mazda cx9. turns out there is a barometric sensor that works with the engine. I went to the dealer after having this massive failure and seems the barometric sensor had failed and the car thought was 2000 meters under water , that made everything to fail.
at the moment that this happened I stopped the car turned it off wait for a minute and restarted. everything went back to normal but seems the whole computer has to be changed.
regards
M
I can't imagine this not throwing a DTC with a Check Engine Light. Did you check for DTCs or did you notice any Warning /
!\ under Mazda Connect > Applications > Vehicle Status Monitor
before you took the CX-9 to the dealer?
Did they specifically tell you that the problem was with the
MAP Sensor (Manifold Absolute Pressure Sensor)? Or, did you hear them say Mass Airflow Sensor?
Ultimately, it is the ECU that determines how much fuel is delivered and thus how much power is made. You say the original symptom was a distinct "power loss." That implies on acceleration the engine simply failed to produce normal power for a specific throttle setting (in general terms). When you step on the accelerator pedal you also change the barometric pressure inside the MAP sensor.
Naturally, the vacuum from the intake manifold puts negative pressure on the MAP and the flexible silicone based chip/diaphragm inside it will report to the ECU a specific level of converted voltage. The ECU takes that signal along with other inputs and then determines fuel delivery. So, if there is a voltage irregularity within this part of the MAP, when you step on the accelerator pedal the ECM may be receiving incorrect signal and that could lead to incorrect fuel delivery causing "power loss" as you describe. The MAP also plays a role on some boosted engines with a turbo charger as the CX-9.
Or, the MAP could be just fine and the ECM/ECU could be the problem in this one regard - which would most like require replacing the entire unit. The other variable inputs to the ECM/ECU for fuel deliver are Air Temperature and Engine Speed - both of which have their own sensors that should be checked for a full diagnostic run. If there is a faulty Higher Temperature input, the ECU/ECM will dump less fuel and that too could cause your "power loss." If a faulty Low Engine Speed is being sent, then again, less fuel will be injected and thus less power made.
The MAP might be one of the easier fixes on this engine. But, I am surprised that no DTC was thrown and that the Mechanic made no mention of an OBDII code which probably would have been one of the first things they checked.
You say the "whole computer has to be changed." That sounds like they are removing and replacing the ECU/ECM and if that is the case, my question would be a resounding why. I could see a faulty MAP sensor. I would have a harder time reconciling a faulty ECU/ECM this early in the life of the vehicle. Possible? Yes, sure it happens. But, I would not like to hear that they had to replace such a mission critical unit this soon.
Can you please report back what specific part they actually replaced once the repairs are made. Thank you.