Powertrain control modules can be located in a variety of places depending on the make, model and year of the car. PCMs are often buried under or behind components in the instrument control panel, consoles, heating and air conditioning systems, and seats, which may require removal to gain PCM access.
If a mechanic suspects that a car has a failing PCM, he needs to remove the unit to get the correct original equipment manufacturer number located on the module. He can use this part number, when matched with the vehicle information and its engine specifications, to select the correct replacement PCM. The PCM controls many aspects of a vehicle's operation, and incorrect units do not have the correct programming to control the car properly.