This is a rare ECU from a JDM "SI States" model that came with the B21A. (37820-PK3-900)
The most noticible difference compared to the USDM ECU is that this one lacks EGR support. Allow deleting the EGR system without a check engine light.
This is an OBD1 ECU that will work with any USDM Prelude that came with the B21A1.
