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What Is a PCM, ECU, Immobiliser or an Engine Computer?

Educational  ·  January 14, 2019

What Is a PCM, ECU, Immobiliser or an Engine Computer?

Your car is made up of thousands of components that work in sync, thanks to the PCM. Most car owners do not bother with the details because, to them, what's important is that the vehicle works. This is fine, however, if you know what's going on under the hood, you will be in a better position to look after your car. 

What Is a Power Control Module or PCM?

The PCM, aka Power Control Module of your car, is a critical automotive part or combined control unit. It is similar to the human brain, which controls and also coordinates the different functions of the entire body. It acts as the brain of your automobile system, it controls and also coordinates the functions of the various sub-systems of your car.

PCM subsystems

Usually, the PCM consists of two sub-systems, which are the engine control units (ECU) and transmission control units (TCU). The major function of the engine control module or unit is to ensure the optimum engine performance by controlling a set of actuators on the internal combustion engine of your cars. The TCU or transmission control module takes inputs from the engine sensors or TCU to change the gears for the optimum engine performance thereby fuelling the efficiency of your cars.

The power control module gets inputs from the sensors which are spread around the car and which gives necessary information related to the engine management as well as performance. 

The other subsystems controlled by PCM include fuel injection, fuel emission, automatic transmission, and anti-lock brake system.

PCM alerts the driver about subsystem issues

Since the power control module controls the different subsets of your car, whenever there is an issue with a subsystem or auto car part, it is the responsibility of the PCM to alert the driver. The driver understands the signal and takes appropriate corrective measure so as to rectify the problem.

For instance, if there is a problem with the transmission system of your car and this problem has resulted in high transmission temperature, the CPU will indicate that the temperature is high. You will then use transmission cooler suitable for your car make and model to fix the issue.

PCM efficiency is crucial

The efficiency of your PCM is crucial so that it picks up signals immediately from the subsystems whenever there is an issue and alerts the driver. If the brain does not function appropriately, the entire sub-functions properly in the human body can be disrupted. Likewise, if the PCM does not function appropriately, you won’t be able to observe the faults or damages in your vehicle, and the different sub-systems of your car will not be able to communicate with one another. This can result in serious damage to your car.

What causes damage to the PCM?

Your PCM can be damaged as a result of several factors. This includes wear and tear, thermal stress, corrosion, and others. The PCM can also be exposed to corrosion as a result of water. This should be prevented because it will affect the longevity of the PCM.

Additionally, the PCM can be damaged as a result of short circuits and voltage overloads in the actuator circuits and solenoids in your car engine. In the case of short circuits, you can get the actuators repaired to fix the issue.

What are the symptoms of a damaged PCM?

Whenever you get a “Check Engine” light, the first thing to do is to check the engine sub-system. If all the systems are in perfect condition, the next possibility can be a damaged PCM. Apart from this, if you experience trouble while starting or running your car, poor engine performance or stalling of your car engine, remember these can be as a result of a bad PCM in your car.

If you have problems starting your engine in the morning, it could be as a result of a damaged PCM or the engine control units. After a proper diagnosis of the other engine parts, if you are completely convinced that your PCM is damaged, the best thing is to replace your PCM either completely or partially. 

Partial replacement of PCM

In most cases, once the PCM is damaged. Rather than replacing it completely, we can identify the damaged subset of the PCM and replace just the part rather than conducting a complete replacement. The remaining units can be reassembled, after which the PCM can be used again. However, it may be difficult to identify the damaged subset for a complicated model of PCM. In such cases, ensure you get help from a professional mechanic.

Your car's PCM is unique to your car and should be replaced with the PCM designed for the same make and model. If the PCM is not replaced with the appropriate model, it will not function properly. You can request CarPart to find a PCM specified to your car's make and model.

Tips for replacing a damaged PCM

The first thing is to locate the position of the PCM in your car. The PCM of some models of car can be buried under other components. Next, disconnect the terminal of your battery and then replace your new PCM. You can replace the battery terminal afterwards.

For some car models, after disconnecting the battery terminal, the PCM needs to go through a recleaning procedure. A small scan tool is required to reprogram the PCM. In some models of cars, it may take some time for the new PCM to adjust to the different subsystem and have complete control over the sub-systems. If you observe that the check engine lights are still on or you get a malfunction indicator after replacing your PCM, there is something wrong. Take your car to a mechanic immediately.

The health of your automobile power control module plays a crucial role towards the overall health of your car. For an effective functioning of your PCM, it should be maintained in an appropriate manner. You shouldn’t overlook any symptom, and if you fail to diagnose the problem, you should visit a reputable mechanic.

Some engine management systems are part of complete immobiliser kits, especially the ones for vehicles manufactured after the year 2000. These kits can include different components, like the vehicle key (which has a reader hidden inside it), a key reader which is usually a black ring around the ignition barrel, and a BCM (body control module). Some of the mid-2000 Jeeps like the WH Grand Cherokee immobiliser kits include the steering column. In the Holden TK Barina you must supply the instrument cluster when supplying a complete second hand ECU kit. 

If you enjoyed this article you might want to check out Does it pay to source your parts yourself or get them brokered by a professional? or How does a water pump work?

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