ECM - ENGINE CONTROL MODULE:
An ECM is an engine control module, sometimes referred to as an engine control unit (ECU). This computer takes incoming sensor data and uses that information to alter the function of electronic systems for better performance. The first ECMs introduced in the early 1980s could only control fuel injection, but as electronics and engine design have improved, the function of these devices has spread to almost every
aspect of operation.
In a modern engine, the ECM will gather information from the intake, exhaust, cooling system and several internal components to judge the running condition of the engine. From there, it can decide the position of the camshafts, the throttle position, ignition timing, fuel injection timing and, in turbocharged cars, waste gate pressure.
PCM - POWERTRAIN CONTROL MODULE:
The Powertrain Control Module the PCM is essentially the ECM and the TCM combined into a single module. Although it may appear like a single unit from the outside in most vehicles, it typically is actually two separate units (the ECM and TCM) housed together.
Through both of these systems, the PCM gets inputs from the sensors which are spread around your car and which give information related to Engine management and performance. The other subsystems controlled by the PCM include the Fuel Injection, Fuel emission, Automatic transmission, and Anti-lock brake systems, and so on.
Both the ECM and TCM operate independently in most cases, but because they are housed in a single PCM module, they are able to easily and efficiently share data and work together in tandem when it is necessary. With both the ECM and TCM together in a single unit, PCMs can better synchronize the functions of each one for better power delivery, fuel economy, and overall efficiency.
Symptoms of a Damaged ECM or PCM
1. Inconsistent engine operation: The ECM and PCM control engine functions that must work together to efficiently burn fuel. When the engine stumbles, coughs, or stalls, it can be caused by the PCM or ECM not regulating the mixture of fuel or the firing of ignition components.
2. Transmission shifting problems: Another common system of a damaged PCM is an automatic transmission that does not shift correctly. The PCM monitors and controls the shifting functions of a modern automatic transmission. In older vehicles, this function falls on the TCM. Either way, if you're experiencing shifting issues, it could be the PCM or TCM being faulty.
3. Vehicle will not start: When you attempt to start the vehicle and it cranks over but does not ignite, it could be due to a faulty PCM or ECM.