In General Motors vehicles, an ECM is an Electronic Control Module. It is a vehicle's computer system. An apt metaphor would be that the ECM is the vehicle's "brain." Among many functions, the ECM is responsible for a GM vehicle's diagnostic system. An ECM module is located in the same place for most GM vehicles. It can be found behind the glove box. ECM modules are no longer used. Once the second generation of On-Board Diagnostics become standard in 1996, the module became more technologically complex and is now referred to as a PCM, or Powertrain Control Module.
Prop the GM vehicle's hood open. Remove the negative battery cable from the battery's negative terminal. Wait at least five minutes. You will need the power completely off. Once the negative cable is disconnected from the battery, you will still need to wait. There will be residual power remaining in the vehicle that needs die off.
Remove the GM vehicle's glove box. The process for this will differ by make and model year. For the most part, you will need to disengage some retaining clips, as well as some stops along the side of the box. You may need to remove some screws, especially if the box features exterior hinges connecting its door to the dashboard.
Remove the retaining bolts on the ECM itself. The number of bolts may also vary by vehicle. The bolts can be removed with a socket wrench.
Pull the ECM forward from retainer where it was mounted. Exercise care in doing so, since the electrical components are still attached to the module.
Disconnect the wiring. This should most be cromprised of the ECM's two harness connectors. It will be fully disengaged at this point.
Remove the ECM completely.
