Make sure the car is off.
Pull the ECU and make sure the rotary knob is turned all the way counter clockwise.
Turn the key to "ON".
Turn the knob fully clockwise.
Wait and count the blinks like an SOS code (note* some ECU's dont have a diagnostic LED).
If you read a code 55 (blink,blink,blink,blink,blink....blink...blink... blink...blink...blink, then everything is ok.
After you're done pulling codes, return the knob back to the counter clockwise position.