The PCM, or powertrain control module, for cars is located in the engine compartment. Replacing the PCM must be done carefully to avoid damage to the new unit, as it is susceptible to shocks from falling as well as electrical shock. The PCM of a vehicle should be replaced with an identical unit, either new or refurbished. Due to the sensitive nature of the component, you should not replace a faulty module with a junkyard PCM.
Disconnect the negative terminal from the battery with the socket wrench, and then allow the vehicle's electrical power to discharge for 10 minutes before attempting to remove the PCM.
Unbolt the power train control module from its place on the coolant overflow reservoir, firewall or passenger-side fender of the vehicle, depending on your make and model, using the 1/4-inch drive socket set, retaining the bolts to use when installing the replacement PCM.
Hold the PCM firmly with one hand while with the other hand you remove the screw that holds the wiring harness into the PCM.
Press the retaining clip located on the top of the wiring harness that acts as a secondary means of holding the wiring harness on the PCM, and then pull the harness straight back away from the PCM. Installation of the replacement PCM is the opposite of the the removal process.
