Car Computer Diagnostics

Your car's owner manual will show you how to plug in the diagnostic tool. If not, search online.

Your car’s owner manual will show you how to plug in the diagnostic tool.  Most are located under the instrument panel on the driver’s side. If not, search online.

The Fix-It Club can show you how to diagnose your car computer to discover issues before they become problems. There’s much your car’s computer can tell you about your car’s condition — if you know how to test and read it. Here’s how to perform car computer diagnostics.

Car Words

A car’s computer is an electrical device that can red reports from sensors at various locations on the car and respond appropriately. Specific instructions are programmed into the computer at the factory. In addition, code readers are available that can help you learn what the computer knows and how it responds.

So what is it that your car’s computer does? It sends out signals to and receives signals from sensors installed throughout your car. These sensors are reading and adjusting fuel, air, spark, emissions, temperatures, and just about everything else going on. In fact, car computers are more accurately called an engine management computer, computer command control system, or engine control computer.

Your car’s owner’s manual or service manual will tell you where the car’s computer is and how to access it. Some car computers allow you to read diagnostic test results. Others only tell you if something goes wrong. Some only require that you turn the ignition key to ON and perform some type of ritual (press this button while holding your ear lobe) to have data displayed on the control console. Others require that you plug in an Onboard Diagnostics (OBD) device that reads and interprets the computer’s data for you.

The diagnostic tool will read out codes for problems the car computer is aware of.  Documentation will help you interpret the codes and solve the problem.

The diagnostic tool will read out codes for problems the car computer is aware of. Documentation will help you interpret the codes and solve the problem.

For example, one popular diagnostics unit ($90-$150) can read computer codes on nearly all 1996 and newer cars. (Actually, it also covers some earlier models and even most diesel engines.) It has adapters to plug into the car’s computer and read:

  • Diagnostic trouble codes (DTC)
  • Generic engine codes (PO)
  • Emission codes (PI)

The codes aren’t much good without an interpreter, which can be the car’s service or technical manual or an after-market book. Just make sure it covers your car including the engine, transmission, and other specifications. That’s how you can perform car computer diagnostics.

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