P03A1: Cylinder 2 pressure-sensor low input and shared-fault clues

P03A1 is the cylinder 2 pressure-sensor circuit low code for this Mazda SKYACTIV-X system. Detection requires an input of 0.29 V or below for five seconds.

Look at the other pressure channels

The procedure checks P0397, P03AB and P03B5 before the isolated number 2 sensor branch. If another low-input channel is present, the factory route moves toward the PCM connection. That is a useful warning against interpreting several simultaneous pressure codes as several independent failed sensors.

For an isolated P03A1, Mazda examines the number 2 connector and sensor resistance. Circuit checks then consider a grounded supply or signal, signal-to-ground cross-connection and an open supply or signal. The page's low-input designation therefore does not uniquely identify a shorted signal wire.

Voltage does not equal compression

The measured condition is electrical. It provides no direct proof that cylinder 2 compression is low, and it should not trigger mechanical engine work without separate evidence. The manual includes a later sensor function inspection in addition to resistance inspection.

Because pressure feedback is unavailable, Mazda inhibits EGR and SPCCI, stops combustion feedback and retards timing. Confirmation uses the appropriate key-on or running self-test and checks the pending record. Preserve the code pattern before clearing it, and verify the exact engine wiring and sensor procedure before performing component tests.

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.