Access to the ECM for all models is through the glovebox on the right front corner of the passenger compartment, where you have to remove the glovebox to get to it. When the engine is running, hit the computer repeatedly by hand to test it, but be careful: this might make the engine struggle, halt completely, and show problems on equipment that reads engine data. If the engine controller module fails the test, look for damage at its electrical connectors. The connectors are color-coded to match the ports in the computer body. Take the computer to a qualified shop if you see no obvious problems. The 4Runner's ECM is right behind the glove box. Unplug the cable from both the negative battery and ECM electrical connectors, but always operate with a conductor when dealing with the computer. Unscrew the bolts keeping the ECM in place, and take out the unit carefully. Install this part the exact way you took it out.