Car Trouble Codes Decoded


We all know how frustrating it can be when our cars don’t seem to be running right. Sometimes it’s a quick and easy fix, while other times, it looks like a total mystery. If you’re having car trouble and are trying to figure out what’s wrong, one place to start is by looking at the error codes that your car’s computer may have generated.

These codes, also called trouble codes, are read by plugging a unique diagnostic tool into your car’s onboard diagnostics (OBD) port. This port is usually located under the dash on the driver’s side of the vehicle. Once the tool is plugged in, it can read the codes and give you a starting point to help diagnose the problem.

The First Letter

The first letter indicates where exactly the car is at fault, which can help narrow down the problem.

The second letter is a status code that tells you if the problem is currently happening or if it’s a historic code that has been recorded by the car’s computer in the past.

P Code – Powertrain

This category of codes indicates a car’s engine or transmission problem.

B Code – Body

This category of codes indicates a problem with one of your car’s body systems, such as the doors, windows, or mirrors.

C Code – Chassis

This category of codes indicates a problem with your car’s chassis, which includes the suspension and brakes.

U Code – Network

This category of codes indicates a problem with the car’s network or communication system.

For example, if you have a P0300 code, the third letter would tell you which cylinder is misfiring.

The First Number

The first number after the letter codes is a sequence number. This is helpful if you have multiple codes, as it can tell you the order in which they were generated. They include:

0 = Standardized (SAE) fault codes

1 = Manufacturer specific codes

The Second Number

The second digit indicates which car system is responsible. There are eight categories.

0 = Fuel and Air Metering and Auxiliary Controls

1 = Fuel and air metering

2 = Fuel and air metering (injector circuit).

3 = Misfires or ignition systems

4 = Auxiliary emission control

5 = Vehicle speed control and idle control systems

6 = Computer & output circuit

7 = Transmission

Third and Fourth Numbers

The third and fourth digits serve only to identify the fault code.

In this example, we can see that P0303 is the DTC.

P = Powertrain fault

0 = Standardized fault

3 = Misfires or ignition systems

03 – Misfire on Cylinder 3

Here are some standard trouble codes decoded:

P0300 – Random Misfire Detected

This code indicates that your car’s computer has detected that one or more cylinders are misfiring. This can be caused by a variety of things, such as a spark plug or ignition coil failure, a fuel injector problem, a vacuum leak, or a problem with the compression in the cylinder.

P0171 – System Too Lean (Bank 1)

This code indicates that the car’s computer has detected that the air/fuel mixture in the engine is too lean. This can be caused by various things, such as a vacuum leak, a dirty or failing mass airflow sensor, or a problem with the fuel injectors.

Now that you know how to read the codes and what some of the standard codes mean, you can use this information to help diagnose the problem with your car. If you need further assistance, feel free to contact a qualified mechanic.