Started as a DPF light flashing problem.

After removing and cleaning the DPF then the engine light started coming on and the engine loses power.

Drives normally for about 5kms then brings engine light on and loses power.

Vehicle came to us from another workshop. Logs code P0154 - A/F Sensor circuit no activity . They replaced the AMM/MAF (air mass meter) and the air/fuel sensor. Subsequently we replaced the EGR valve and the turbo boost/barometric pressure sensor.

Bit of History :
The vehicle had gone in because the DPF light was flashing.
They removed, cleaned and refitted the DPF, and the A/F fault came in on test drive after that.
They replaced the AMM sensor and the A/F sensor but the fault remained.
Engine oil level was very high on arrival.
We have replaced the air filter, engine oil and oil filter, the EGR valve and the turbo boost/barometric pressure sensor.
Regenerated the DPF - no change to fault.
We have gone through both Denso's and Mazda's diagnostic procedures for this fault code without identifying the cause of the fault.
Various components have been replaced as stated without resolving the fault.
The engine compression is a bit low compared to data? we measured 360PSI on all 4 cylinders (engine warm) verses minimum spec of 391PSI.
We note the EGR valve is not moving under workshop conditions - not opening/closing at idle/when revved up - EGR valve was replaced made no difference. EGR valve does respond to scan tool commands.
We note the barometric pressure reading is 64kPa at any RPM, while the intake manifold absolute pressure varies with engine speed but over 100kPa.
Ignition on supply voltage to baro sensor is 5.05V, pin 3 & ground voltage is 25.2mV against Denso spec of 0.3V approx. and the pin 2 & ground voltage is also low, 1.12V against spec of 2.5 to 2.8V.
IAT/MAF sensor supply voltage is 12.4V. The pin 1 & 2 resistance is low 1.63kOhm verses Denso spec of 2.21 to 2.69kOhm. The pin 4 and ground voltage is low, 15.1mV verses Denso spec of approx. 0.3V, and the pin 3 & ground voltage is slightly high - 2.18V verses Denso spec of 1.7 to 2.1V.
Electronic throttle control commanded and actual angles are always around 80 degrees with engine running.
no history of any system re-flash or emission deletes,
Numbers we have for the differential pressure sensor are as follows:
DPF differential pressure at 0 RPM: 0.03kPa
DPF differential pressure at 774 RPM: 0.96 kPa
DPF differential pressure at 2061 RPM: 2.94 kPa
Differential pressure sensor correction at 0 RPM: -104Pa
Differential pressure sensor correction at 774 RPM: -104Pa
Differential pressure sensor correction at 2000 RPM: 156Pa