The trans valve body parts are included with the automatic transmission components that power an engine's transmission. Although there are a variety of parts that work together, each one is specific to the Mazda 3 and need to be replaced according to factory recommendations. This ensures the part will fit and work.
Over time, the parts of a transmission wear down. Many of the elements of the trans valve body are manufactured to resist corrosion, and they're crafted from durable materials. However, when making a complete transmission repair or working with other components, replacing these minor parts increases the lifespan of the Mazda 3 engine.