P2311: Cylinder 4 secondary-ignition code interpreted through ion sensing

P2311 generally identifies ignition coil D secondary circuit. The documented Mazda SKYACTIV-G monitor instead names the specific measured function: number 4 ion-sensor circuit behavior.

What the PCM actually observes

After the engine starts, an erroneous signal from ion sensor number 4 at 2,000 rpm or below can trigger the code. The source does not supply a single voltage threshold for that signal error. It also lists cylinder 4 misfire, so the DTC should not be translated directly into a coil replacement instruction.

Mazda's first code-specific branch checks P0304 and follows the misfire procedure when it is present. Only then does the flow investigate the coil/ion-sensor connection, F8 15 A supply fuse and the supply, ground and signal wiring.

Keep the electrical paths distinct

A missing ground, an open supply and a signal wire held at power can all prevent valid ion-sensing information, despite requiring different repairs. The manual therefore checks these paths separately and evaluates the sensor itself after external circuit problems have been considered. PCM connector trouble remains part of that investigation.

There is no special fail-safe listed for this page. The repair-completion test is engine-running, followed by a pending-fault check and review of other DTCs. Retaining the original cylinder 4 misfire context makes that comparison meaningful. Confirm the exact engine wiring and cylinder identification before any ignition-system component testing.

Documented application

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