The "check engine light" on a Mazda three is located to the left lower side of the tachometer. It is orange in colour.
The 2004 Mazda MAZDA3 has an inline 4 engine.
The 2004 Mazda MAZDA6 has an inline 4 engine.
Yes.
The 2004 Mazda MAZDA3 has a 2.0 L base engine size.
The 2004 Mazda MAZDA6 has a 2.3 L base engine size.
Talk to your Mazda dealer but, it sounds like a problem with your automatic transmission and just like a check engine light it may be a number of problems.
Only with scanner through eobd plug
The "Reduced Engine" Warning Light alerts drivers when/if there is a serious problem with the transmission and/or one or more of the engine system components.
The 2004 Mazda MX-5-Miata has an inline 4 engine.
The 2004 Mazda MAZDA3's engine produces 148 hp @ 6500 rpm.
The 2004 Mazda MAZDA6's engine produces 160 hp @ 6000 rpm.
You need a new transmission.