where is ecu located?

[CoasTek240]

where's the ecu located on an s13?

[AceInHole]

its' behind the passenger side kick panel.  
take off the panel under the dash towards the front of the car in front of the passenger side door.

[geeaj]

Yes, its called a kickpanel. The ecu is held together my 10mm bolts, one bracket on each side. Loosen all the bolts and you can rotate the ECU 180degrees without unplugging it (if your checking codes).