P053C: Crankcase heater voltage stays high after the relay is switched off

P053C is the PCV-heater high-input code. In Mazda's SKYACTIV-D implementation, it refers to the blow-by heater supply staying above specification while the relay is commanded off.

Command state defines the failure

The preconditions include battery voltage between 8 and 16 V and at least half a second after ignition on. The high supply must continue for five seconds. A heater receiving voltage while intentionally energized is not the same condition; the disagreement occurs during the commanded-off state.

The source lists a faulty relay, a relay-control circuit short to ground, powered heater or monitor wiring, connector trouble and a heater or PCM malfunction. A grounded control wire can keep a relay energized, so the high-input label does not imply that only the heater feed itself is shorted to power.

Establish why the supply remains present

Mazda inspects the relay and PCM connection, then the relay control path and heater-side connection and supply before evaluating the heater. This helps distinguish a relay that remains active from unwanted power reaching the output circuit elsewhere.

The page lists no separate fail-safe. Confirmation uses the applicable self-test and another pending-code inspection. Preserve the original relay command and monitored supply relationship; merely observing heat or battery voltage at the heater without the command context cannot confirm this specific fault or prove its repair.

Documented application

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