The ECM (electronic control module) in a car is the vehicle's brain. The ECM is responsible for receiving and transmitting signals to all the sensors in the vehicle. When the ECM goes bad, it can cause the car to run erratically, if at all. Replacement takes just a matter of minutes, as the ECM is easy to access. The location of the ECM depends on the make and model of the vehicle. In most vehicles, the ECM is located in the engine compartment. Some vehicles have the ECM mounted under the driver's or passenger seat, however.
Open the engine compartment to access the battery. Disconnect the battery with a socket wrench.
Locate the ECM either in the engine compartment or under one of the front seats in the vehicle. The ECM is a silver, rectangular module. Consult your owner's manual or appropriate car dealership for the location of the ECM if you don't know.
Disconnect the electrical supply by lifting the locking tab and pulling away from the computer. This will isolate the electrical power.
Unbolt the screws holding the ECM in place with a socket wrench. Pull the old ECM out and replace it with the new one.
Bolt the ECM in place with the socket wrench. Ensure the bolts are tight.
Plug in the electrical wires to the ECM. The wiring harness will lock in once it is pushed in far enough.
Connect the battery cables to the battery. Tighten the cables with a socket wrench.
Start the vehicle and allow it to idle for five minutes. If there are still conflicting codes, the "Check Engine" light will come on.
Some vehicles will require a reset code for the radio. Contact the dealer to find out what the codes are and how to input them. A scan tool can be useful for determining if the ECM is bad and if the new ECM fixed the problem.