P2104: Mazda diesel idle-control diagnosis includes boost and vacuum faults

P2104 is generally labeled throttle actuator control forced idle. Mazda's SKYACTIV-D page describes intake shutter idle-air control and evaluates exhaust or boost pressure at or above the PCM's estimated value under its specified operating conditions.

Do not assume a throttle-body-only repair

The source's possible causes include variable-geometry turbocharger control, vacuum plumbing, the turbo solenoid and actuator position sensor, MAP and exhaust-pressure sensing, fuel injectors and oil entering the combustion chamber. The exact transmission-state wording is application-specific and should be verified against current service information before reproducing the event.

Mazda compares requested turbo position with actual position using scan-tool control. If position does not follow, the route includes vacuum lines, the chamber, check valve and solenoid before a turbocharger decision. A pressure-sensor error can require a different repair from loss of actuator vacuum.

Oil and aftertreatment evidence also matter

The procedure includes oil-level inspection, injection correction and controlled aftertreatment service after the applicable fault diagnosis. Oil above the specified dipstick limit is not treated as an incidental observation. These branches explain why a generic forced-idle definition does not cover the complete Mazda diagnostic.

Turbo actuation, diesel regeneration and any suspected oil ingestion require professional evaluation. This article does not recommend initiating regeneration or a road test on the code alone. Confirmation follows the supported repair and captured conditions, using safe data collection and the exact vehicle procedure.

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.