Why Do Car Computers Break?
Dodge Engine, controlled by the PCM
Starting in the early 1990s, automobile function – particularly the engine and powertrain – were integrated with controls processed by an onboard computer named by Dodge as a PCM. This is an abbreviation for Powertrain Control Module. Prior to the advent of this type of computer, automobiles usually had an installed ignition module that replaced the even older distributor mechanisms. The engine control units on most American car models were known as ECU modules, but by the mid-1990s the fancier, more complex computer units combined the ECU with the PCM.
How The Sensors Were Connected To The PCM
The modules designed for use in domestic car models in the 1990s were information processors that received input in the form of electronic signals from the various sensors located on the engine. This information was then sent from the processor unit to system actuators. The fuel injection control, voltage regulation, engine temperature readings, and other vital data was processed through the PCM, with special coding assigned to each of the various functions.
One of the big breakthroughs in the 1990s was the development of a module that could immediately turn input signals into output data to control how the vehicle would respond to ignition. The air temperature, air pressure, coolant temperature, and oil level was measured in order for the output signals to instruct how the initial fuel mix was to be determined. This made cold weather starting much more reliable.
Problems With The Installed PCM
Most car manufacturers designed a specified model of PCM/ECU computer unit for a certain car model. The input signals were interpreted correctly only if the sensors were the originals. Aftermarket products could have a negative effect on these microprocessors. Also, irregular voltage spikes could cause readout errors within the module. Sometimes, troubleshooting the module would result in the discovery of burnt-out circuitry caused by moisture intrusion.
Fuel injectors and ignition coils sometimes developed faults that could actually burn out the coil drivers in these early-model PCMs. Almost any type of electrical overload could cause faulty input readings. This problem was not solved until the early 21st century models were developed and released. Most PCMs manufactured after 2003 had built-in overload protection.
Today’s modern PCMs are far more reliable. However, prior to 2004, most car models would nearly always contain a default alert in the PCM that would light up the “check engine” display on the dash. The problem was that car owners would not know if the trouble was with the engine or the PCM itself.
Replacement of a faulty PCM in a pre-2003 car model involves a procedure known as reflashing. Because the computer is connected to a set of sensors located on the engine and transmission, this process is necessary in order for the computer to properly connect to and read information coming from the other sensors and modules located throughout the vehicle.
