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What is PCM in a Car?

  • Author :
  • TATA AIG Team
  • Published on :
  • 17/04/2024

Most modern cars are made of complex machinery that features various computer controls. These computer systems control the functioning of the car in different ways. In older cars, the Engine Control Module (ECM) and Transmission Control Module (TCM) worked independently as computer onboard systems. In present-day scenarios, we see a PCM in a car that is a combination of ECM and TCM.

If you own a vehicle, you need to know what automobile PCM is, how it works, and much more.

What is PCM in a Car?

Let us begin by knowing the PCM's full form in the car: the powertrain control module. It controls the various computer systems in a car to ensure their smooth functioning. The PCM can be defined as the brain of the car as it manages the engine, transmission, and all other systems in the car according to the information received from various sensors.

PCM is known to control two main components of your car:



The PCM is connected to every sensor in the car and makes decisions based on the signals it receives from each sensor. In simple terms, a PCM is a microprocessor in modern cars that controls all the car's functions, from the power windows to the fuel mixture.

How Does Automobile PCM Work?

The powertrain control module primarily works based on the signals and information received from the various computer-based car components.

Some of the in-built computer systems that send data to the PCM in a car are:

  • The Throttle Positioning System

  • The Check Engine Light

  • ABS Braking System

The PCM works in the following manner:

  • Monitoring—The PCM monitors various functions, such as the speed at which the wheels turn, the airflow to the engine and out of the exhaust, the temperature of the coolant, and so on.

  • Passing the Signals—After receiving information from the various systems, the PCM passes it to the microprocessors, which then make sense of what is happening in the car.

  • Decision Making—Once the PCM receives information on what is happening in the car, it makes hundreds of decisions in a split second, such as firing the spark plugs, injecting fuel, determining how much fuel is required in each cylinder, and deciding when to shift the automatic transmission to a different gear.

  • The PCM makes all these decisions after much calculation and setting adjustments to ensure the car's efficient functioning.

Functions of a PCM

The primary function of the PCM is to manage all other functions in the car so it can run smoothly. Some of the functions it handles include:

  • Idle Speed

  • Ignition timing

  • Error monitoring

  • Transmission Control

  • Air-to-fuel ratio

  • Keeping the PCM well-maintained and protected is essential for road safety and the smooth functioning of the car. Most of the modern cars have the PCM located in the engine bay. In some car models, we may also find it near a car’s windshield.

Why Should Your Replace the PCM

The PCM is your car's central computer system, controlling the engine and performance. However, a voltage overload can lead to short circuits and PCM failure. The PCM receives data from the check engine light system and also controls it. Therefore, the car alerts the driver about PCM failure by illuminating the check engine light on the dashboard.

The PCM cannot be repaired if it malfunctions and, hence, needs to be replaced with a new one. Once the PCM fails, the car’s engine performance and various other functions begin to drop. Therefore, one must immediately replace the PCM to improve the overall engine handling and car performance. The PCM replacement cost can vary as per the car model and variant.


The PCM takes all the critical information from the other components of the car and makes decisions to ensure that everything works smoothly. However, if the PCM automobile fails, many functions can go haywire. Therefore, the PCM must be immediately replaced if it malfunctions.

While PCM ensures your vehicle’s optimum performance, a car insurance policy protects against damage and third-party liability in case of an accident. Insurance from Tata AIG is an excellent choice as we offer various plans to suit customer requirements.

We offer insurance plans at the best rates with plenty of benefits. You can use a car insurance calculator to find out the insurance price for your vehicle and determine whether it fits within your budget.

While choosing car insurance, you must analyse the benefits and costs to gain the maximum advantage from it.


What are the symptoms of a bad PCM?

The most common indicator of a bad PCM is the check engine light illuminating the dashboard. Some other symptoms include:

Poor fuel economy

The vehicle won’t start

Engine performance issues

Is PCM and ECU the same?

ECU and PCM are interconnected as they perform various functions in modern vehicles. PCM, or powertrain control unit, combines the functions of the ECU (engine control unit) and TCM (transmission control unit) to optimise vehicle performance.

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Disclaimer / TnC

Your policy is subjected to terms and conditions & inclusions and exclusions mentioned in your policy wording. Please go through the documents carefully.

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