Trying to repair my ECU.

It is possible to test the transistor using diode setting on multimeter. There is an intrinsic diode drain to source as shown in data sheet. Check that with diode test. Bad part is most often low Ohms, both polarity. Using Ohm setting, check gate to source, often 10K or greater, in circuit. The 10k or more is a pulldown, to avoid gate float during bootup.