P03A0: Cylinder 2 pressure function differs from a circuit-limit fault

P03A0 is Mazda's SKYACTIV-X cylinder 2 pressure-sensor function fault. It indicates that the pressure behavior fails a plausibility test, even though the prerequisite sensor signals are suitable for running that test.

What is compared

The controller estimates compression pressure from intake pressure near intake-valve closing, then compares that estimate with the measured value. It separately evaluates peak-pressure timing and pressure behavior on either side of top dead center. A function failure therefore includes more possibilities than a sensor voltage simply being too high or too low.

Fuel cut, closed EGR and inhibited purge form part of the diagnostic context. Mazda also requires valid crankshaft and camshaft information and excludes the corresponding cylinder-pressure circuit faults. Ignoring those conditions risks interpreting normal combustion variation as this monitor's failure.

What the diagnostic branches mean

The source checks whether multiple pressure-function codes are present, then assesses connections, sensor circuitry and the sensor itself. It also considers fuel-system faults and engine compression. A cylinder-specific code narrows the location, but does not establish that the sensor is the only possible cause.

Protective actions disable SPCCI and EGR, stop combustion feedback and retard ignition. A repair should restore credible cylinder 2 pressure behavior under the specified monitor conditions, followed by a pending-code check. The factory deceleration confirmation belongs in a controlled professional road test, with safe data recording rather than driver-operated scanning.

Documented application

Mazda3 workshop manual 01/2019 onward, d9n1-1a-22d_ver10; PCM (SKYACTIV-X). Verify exact vehicle specification; this is a Mazda application example. Mazda factory diagnostic page, mirrored by CHARM.