What is a PCM? | Symptoms and Causes of a bad PCM

One of the most vital components in your car is the Powertrain Control Module (PCM). The PCM has the responsibility to control the various parts and sensors of the engine. It ensures the proper supply of coolant, engine oil, and air-fuel mixture. It turns ON the check engine light when any engine sensor creates a problem. This article deeply explains PCM function, symptoms, and causes.

What is Powertrain Control Module?

The PCM is known as the brain of the vehicle. The PCM is also known as the engine control module (ECM). It is a self-propelled control system installed in your car.

The main function of the PCM is to collect data from different parts and sensors of your vehicle engine. After collecting the data, it uses data to produce the desired power and efficiency of the vehicle by controlling the engine’s spark and fuel. It works efficiently when there is a proper flow of information from the PCM to the sensors and the sensors to the PCM.

Powertrain control module

Usually, the powertrain control module can be referred to as the integrated controller, consisting of the engine control unit (ECU) and the transmission control unit (TCU). It controls about 100+ functions of your vehicle.

A car has several hundred trouble codes, and every single of them indicates a problem in a specific part of the car. Whenever a car gets into a problem, the powertrain control module generates the trouble code related to that specific problem and illuminates the “Check Engine Light” on your car’s dashboard.

Function of PCM

The car powertrain control module controls several features of your vehicle. However, the following are the major functions of PCM:

  • Efficient fuel delivery
  • Proper mixing of the air and fuel
  • Controlling ignition timing
  • Throttle control
  • Idle speed control
  • Control of emissions
  • Control the turbo boost pressure
  • Ensure the efficient working of the engine

The proper communication of the powertrain control module with the various sensors is the basic key to controlling all its tasks efficiently. It starts by delivering a command to an actuator and calculates the definite results through a sensor.

Function of PCM

PCM acts as a director; it directs each actuator about what to do in answer to a specific command by a car. For example, as the throttle gets hit, the PCM or ECM is designed to know about the satisfactory readings in response to this hit.

Whenever it observes any issue or fault in any part of the car, it instantly warns the driver through the check engine light. It is a programmed device that consists of several connections and designs.  

Symptoms of a bad PCM

Usually, the PCM is designed to last in your car for a lifetime, but several different causes make it faulty. In this situation, you must replace it with the new one. Its life depends on its quality and its manufacturing design.

The probability of permanent failure of your car’s powertrain control module is very low in the latest vehicle models, but it may fail with time. As the powertrain control module goes bad, it generates one of the below-given symptoms:  

  1. Check Engine Light
  2. Reduced Engine Performance
  3. Shifting issues
  4. Issues in starting
  5. Misfires
  6. Failed Emission Test
  7. Poor Fuel Economy
  8. Code Errors related to PCM

1) Check Engine Light

The check engine light is one of the major symptoms of a bad PCM or ECM. However, this light may illuminate due to many other problems in your car. For example, issues with wiring, MAP sensor, IAT sensor, or engine overheating may also trigger check engine light.

check engine light

The best way to check whether it’s a bad PCM or not is to use an OBD2 scanner to scan the trouble codes and find the issues.

Read More: Causes of Check Engine Light Flashing 

2) Reduced Engine Performance

The bad performance of your car’s engine can be the reason for a bad powertrain control module. As the powertrain control module goes bad, it doesn’t properly control the fuel and the spark timing. When the fuel and spark timing disturb, this results in poor performance of the engine. Therefore, a bad PCM may lead to poor power, acceleration, and fuel efficiency in your car.

Engine Performance reduction due to bad MAP sensor

3) Issue in Shifting Gears

A problem in gear shifting is also one of the common symptoms of PCM failure. The PCM controls the functions of the transmission system and the engine of your car. Thus, the issues with the powertrain will indirectly be the issues with your car’s powertrain control module.

shifting issues due to bad powertrain control module

As soon as you detect shifting issues, drive your vehicle to the mechanic to fix it as soon as possible. Also, the unpredictable actions of your car may be the cause of serious accidents in the future.

Read More: Symptoms and causes of Low Transmission Fluid

4) Issues in Starting 

It is the job of the powertrain control module to ensure that every component it controls is working properly. Timings of the ignition are one of these tasks. When the timing is off, the spark plug doesn’t ignite the air-fuel mixture. So, with a bad PCM, you will find it hard to start your vehicle. Furthermore, starting your car in cold weather becomes even more difficult.

Hard Starting Condition due to bad map sensor

5) Misfires

If your car often backfires or misfires, then it needs a proper check-up by a professional. In the service centers, the professional will find the trouble codes and will let you know the exact issue with your car.

Engine Misfiring

However, misfires or backfires most commonly occur due to bad fuel supply or bad ignition in the combustion chamber. Therefore, we can take them as a symptom of a faulty PCM.

6) Failed Emission Test

A healthy powertrain control module ensures the minimum emission of exhaust gases and improves engine performance. However, when the PCM goes bad, it doesn’t control the emission efficiently and increases the emission rate. In such conditions, your car performance will be reduced. This will result in the failure of the emission test of your car.

Emissions Test

7) Poor Fuel Economy

A reduction in fuel economy is often a sign of a bad PCM. When the powertrain control module goes bad, your car couldn’t be able to detect exactly how much fuel it has to burn in the combustion procedure.

Poor fuel economy due bad PCM

Usually, cars with a bad powertrain control module consume more fuel than cars with a properly functioning powertrain control module. So, you may have to pay more for fuel if your car has a bad PCM.

8) Code Errors related to PCM

The bad PCM related trouble code is a most common symptom. A trouble code is created in your car’s computer whenever a car faces an issue. Use a proper OBD2 scanner to read the code. If the code is related to the PCM, then you are lucky that you detected the proper issue at once.

PCM Location

A PCM is a metal box with some wires coming out of it. The position of the powertrain control module varies according to the vehicle model. Mostly, the PCM is installed in the engine bay near the fuse box. In some models, you can also find it on the front windshield after removing a few covers.

If your vehicle’s PCM is not located in the engine bay, then it may be found inside the passenger compartment under some plastic coverings.

Read More: How to change Engine Oil?

Causes of a bad PCM

There are several causes that lead to PCM failure. Following are the major causes of a bad powertrain control module:

  • Engine overheating problems
  • An unbalanced fuel-to-air ratio
  • Incorrect engine timing
  • Thermal stress
  • Short in electrical wirings
  • Faulty sensors
  • Inadequate fuel supplies

Read Also: Compression ratio of Petrol and Diesel Engines

Replacement Cost of PCM

PCM is a computer, and computers are usually expensive. The replacement cost of the powertrain control module varies according to the vehicle model and labor cost. The average cost to replace a PCM is from $945 to $1,040.

The labor cost for PCM replacement is between $60 and $120. You can save labor costs by replacing it yourself, but you need to use software to configure and program the powertrain for this task. So, we always recommend visiting the proper technician for powertrain control module replacement.

There may be a chance to find a used powertrain control module at a low price from a junkyard. But you still have to spend some money on its installation and reprogramming.

Difference between PCM and ECM

PCMECM
A Powertrain Control Module is a computer in your car that controls the engine and transmission to maximize power and fuel economy.An Engine Control module is a computer in your car that just controls the engine.
This part of your car controls almost all the functions of your car’s engine.It controls limited parts of your engine. It regulates and sends commands among these parts.

FAQ Section

What does a powertrain control module do?

The powertrain control module, also known as PCM, is your vehicle’s brain. It manages the engine, transmission, and other systems based on the information it receives from various sensors around the vehicle.

What is reprogramming of a PCM?

Reprogramming the powertrain control module is a software upgrade process that may include resolving issues like stalling, idle roughness, starting issues, and emission failure.

What is the reprogramming cost of PCM?

Reprogramming is far cheaper than PCM replacement. The average reprogramming cost of the PCM is from $50 to $160. It is done by connecting your car powertrain control module with the manufacturer’s software and then updating it with the latest version of it.

It is a simple process that may take about an hour. After the completion, do not forget to check the system is working properly and ensure there are no trouble codes.

Can I drive my car without PCM?

No, you cannot drive without a PCM. As the PCM controls all the tasks of the engine, so it will not be possible to even start your car without it.

How much time is required to get the PCM fixed?

It takes about an hour to fix the PCM software. But if there is a problem with the hardware, it may take several hours to fix.

Can I repair the PCM by myself?

Yes, you can repair or replace the PCM, but you need some special tools for this purpose. These tools will be used only once. So, it is always recommended to visit the service center for this purpose.

Can I replace the ECM by myself?

Yes, you can, but always consult the repair manual before repairing your car’s ECM. You will find the steps you must follow to replace the ECM properly.

What are the causes of a bad PCM?

Following are the two major causes of a bad PCM or ECM:

  1. Voltage overloads (frequently due to a short in a solenoid or actuator circuit)
  2. Environmental factors such as vibration, thermal stress, and corrosion. Water entering the powertrain control module may short circuits and produce irreversible corrosion that damages electronic connection.

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