P03A8: Cylinder 2 combustion assessment cannot be trusted

P03A8 identifies the cylinder 2 abnormal-combustion monitor in Mazda's SKYACTIV-X manual. Its central concern is unreliable cylinder-pressure information used to assess combustion.

The qualifying conditions change the meaning

Mazda runs this check without detected misfire or fuel cut, inside its permitted control region and with the relevant pressure-function and circuit faults absent. The code therefore should not be treated as an interchangeable label for cylinder 2 misfire.

The PCM can determine that the reported combustion value is unreliable or that the sensor signal is abnormal for a sustained period. The source mentions poor pressure-sensor insulation as one way this can happen. It also lists actual engine causes, including incorrect injection timing, injector malfunction, insufficient compression and coolant leakage into a combustion chamber.

A two-sided investigation

The factory procedure observes pressure data for connection-related changes, then investigates sensor wiring and sensor behavior before injector and mechanical checks. An electrical reading within a broad range does not establish that it accurately represents cylinder 2 combustion.

Fail-safe actions stop combustion feedback, inhibit SPCCI and EGR, and retard ignition. Verification belongs after a cause has been established and repaired, using the specified running check and another DTC inspection. The source's related-code list contains typographical defects, so no corrected code numbers are inferred here. Keep the exact cylinder assignment and the supporting pressure, fuel or mechanical finding together in the repair record.

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.