We are reader-supported and we may earn a commission if you buy through our links.

Car CPU Problems: 5 Most-Common Issues & Solutions

The current crop of cars has multiple control modules for the:

  • Engine (engine control module or ECU),
  • Transmission (transmission control module or TCM)
  • Powertrain (powertrain control module or PCM).

Each of these computers can cause issues with drivability, emissions, ignition, and fuel injection.

When they malfunction, they can have significant issues that need to be corrected immediately, so we’ve gathered the most common problems and their solutions to keep your car on the road.

Did You Know?

Computers in cars are nothing new.

Some level of computerization has been incorporated since the late 1960s and early 1970s. By 1990 most cars in the Western world were computer-controlled, which included circuit boards and programmed microchips.

#1 – Your Check Engine Light (CEL) Identifies A Problem

The Check Engine Light is your guide to knowing if any of the computerized systems have identified a problem.

It will illuminate when a problem has been detected, and they can range from something simple like a loose gas cap to a major problem of a computer module going bad.

How to Fix It

Many cars from the 1980s couldn’t relay much information from the computer modules. You could use a diagnostic scanner to see a series of blinking lights, and then you would need to research what it meant.

Today’s cars do a much better job of identifying problems and relaying that information to the driver. Sophisticated scanning tools are available to lead you through the identified issues and the internet can help you repair your car at home for a fraction of the cost compared to a dealership.

The key to fixing identified issues is diagnosing the cause of the problem soon after the Check Engine Light illuminates. A diagnostic scanner will show the trouble codes that can be researched, and the faulty components can be replaced.

#2 – You Have Engine Or Transmission Issues

Your car has control modules, i.e. computers, that communicate directly with the sensors connected to your engine and transmission.

With this information, these computers can adjust how each major component operates. When the control module goes bad, the engine or transmission may start to have issues.

How to Fix It

Each major powertrain unit has one or more control modules that monitor performance and adjust the settings based on the environment and driving conditions.

The transmission may start to shift oddly between certain gears, it may start to slip and not hold power, or it could not go into gear if the Transmission Control Module (TCM) goes bad.

Before assuming the control module is the problem, be sure to check the fluid level and fluid color.

Low fluid levels or fluid that should be changed can cause slipping and poor performance. You may need to take your vehicle to a transmission service center to have the module checked if problems continue.

The Engine Control Unit (ECU) connects to many different sensors on the intake manifold, the exhaust system, and the engine itself. It will utilize all inbound information to adjust the performance of the engine, which can be positive or negative if the module is operating correctly.

When the ECU goes bad, the engine will run poorly, if it will run at all.

You may notice that your car accelerates poorly, the ignition misfires, and it lacks the power it previously had. The idle can constantly fluctuate up and down as it searches for the correct setting, and it may stall the engine without using the gas pedal to add extra fuel to keep it running.

Every major control module or computer in your car has multiple functions, and rarely do these modules go bad. Don’t take that as they are bulletproof though. When they go bad, they tend to cause multiple problems at one time.

If you have a major problem, the ECU or TCM could be the problem. If you have a small problem, always check the related sensors and fluids before assuming the module is faulty.

#3 – Sensor Readings Are Inaccurate

The sensors around your car provide data for the computers and control modules in your car to make informed changes to optimize performance.

If the computer doesn’t understand the incoming readings from the sensors, it may make adjustments that jeopardize the performance and safety of your car.

How to Fix It

You have more sensors in your car than computer modules, but they all must collaborate for the car to run well. Sensors relay information on temperature, oxygen levels, wheel speed, and status of components.

If the computer doesn’t understand the information coming from the sensors, it may default to a basic program and not make adjustments according to the correct programming.

Faulty sensor readings may cause stalling of the engine and/or a no-start condition. Your car may fluctuate between working and being a chunk of steel that does nothing. A faulty control module can allow the car to run but have poor performance and fuel economy.

It may get you from point A to point B, but not well.

It is more likely that a sensor has gone bad and is sending incorrect information to the computer rather than the computer going bad. Before assuming either is the problem, you can use a diagnostic scanner to look for trouble codes stored in the computer.

The code being stored may give you an indication of the problem and if it relates to a sensor. If you don’t have a scanner, most local auto parts stores can use an in-house scanner to read any trouble codes being stored and help diagnose what is causing the problem.

#4 – Diagnostic Tools Don’t Connect To The Computers

Professional mechanics and do-it-yourself hobbyists both use diagnostic tools to communicate with the computers in your car.

The tools use this shared information to relay detected problems and can be useful in diagnosing a problem if they connect to the computer. In rare cases, the computers won’t connect because the computer is faulty.

How to Fix It

Onboard Diagnostics (OBD) have been incorporated since the mid-1980s in many cars, and these systems monitor the operating systems and sensors on the car.

When they detect a sensor that is sending signals out of the designed range, it will log a trouble code and illuminate the Check Engine Light (CEL).

In mid-1995 a second generation of diagnostic systems called OBD-II was launched, and this generation includes more sensor data options and information systems. Over the last 30 years, the OBD systems have steadily added more diagnostic assistance to keep cars running better for longer, but only if they can connect to scanning tools.

If you find that an OBD scan tool won’t connect with any of the computers in your car, check that the connector pins aren’t bent out of position. They can be bent back into the correct position to make contact with the scanning tool connector, which will restore the communication function.

If the connector pins aren’t bent, and the scan tool and cable aren’t damaged, you may need to take your car to a service center to have the computer further diagnosed. Most dealerships have tools that can check computers for programming and determine if they have any faults.

#5 – Your Car Is Displaying False Warning Messages

You may be most familiar with the Check Engine Light (CEL) as it’s the most referenced light that illuminates when a problem is detected. It is not the only one that can illuminate though.

You have multiple warning lights in your gauge cluster, and they can display false information if a computer is faulty.

How to Fix It

The engine and transmission computers are directly related to the Check Engine Light, and when either major component detects a problem this light will illuminate.

Most newer cars have a Body Control Module that retains the settings for other systems like seat belts, airbags, seat position, and lighting.

A bad control module can trigger a warning light to illuminate when there isn’t a detected problem with the system. If your car has a message center or a display that shows words, you may see a warning message for a problem that doesn’t exist.

If you can’t diagnose the problem yourself using a diagnostic scan tool, take your car to a professional service center like a dealership. They should be able to determine if there is a problem with a sensor, a programming issue with the computer, or if the computer has gone bad.

With that information, you can fix the issue and stop looking at a potentially false warning message.

Was this article helpful? Like Dislike
Great!

Click to share...

Did you find wrong information or was something missing?
We would love to hear your thoughts! (PS: We read ALL feedback)