P2305: Cylinder 2 ion-sensor signal error at lower engine speed

P2305 carries the general label ignition coil B secondary circuit. For this Mazda SKYACTIV-G application, the factory diagnostic target is ion sensor number 2, integrated into the ignition-coil/ion-sensor arrangement.

A combustion signal, not a coil verdict

The detection condition is an erroneous number 2 ion-sensor input after the engine starts, at 2,000 rpm or below. Mazda lists cylinder 2 misfire among the possible causes and gives P0302 priority in the related-code branch. If both appear, the misfire procedure can identify evidence that would be missed by treating P2305 as an isolated wiring fault.

The electrical cause list spans the F8 15 A fuse, the sensor supply and ground, its signal conductor, the connectors and the PCM. Both a signal short to power and a signal short to ground are possible, so the code itself does not tell which electrical direction occurred.

Follow the complete signal path

The workshop flow separates supply integrity, ground continuity and signal-circuit integrity before evaluating the sensor. These are different failure mechanisms even though the same ion-sensing error reaches the PCM. The correct cylinder identity also matters: the source assigns this particular DTC to number 2, rather than an arbitrary coil chosen by location.

Confirmation calls for the running self-test and another pending-code inspection. Preserve the initial misfire and ion-sensor records, and use Mazda's applicable ignition-system procedures for testing rather than assuming a parts swap proves the diagnosis.

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.