What Do Those Diagnostic Codes Really Mean?

February 26, 2018 Published by Leave your thoughts

It’s understandable to become anxious if your “check engine” light turns on, but the problem might not be severe. Understanding diagnostic codes will help you better determine what the underlying problem is with your vehicle.

Here’s some information from a mechanic in Lubbock, TX about diagnostic codes in vehicles.

About the diagnostics lights and displays

The check engine light, also known as the “malfunction indicator lamp,” appears when the vehicle needs to warn you about a problem detected by your onboard diagnostic system. This indicator occurs when you have a problem that could cause your vehicle’s emissions to rise to a level of 1.5 times the legal limit.

In many cases, you will have a trouble code displayed, an alphanumeric value that indicates a specific type of issue in your vehicle. The code is used by all vehicle manufacturers who are required to comply with OBD emissions regulations in the United States, and the list of those codes was developed and standardized by the Society of Automotive Engineers (SAE).

There are four primary categories of diagnostic trouble codes:

  • Powertrain codes: “P” codes, having to do with the engine, transmission and emissions systems
  • Body codes: “B” codes, having to do with lighting, airbags and climate control
  • Chassis codes: “C” codes, having to do with electronic suspension and steering systems and the antilock braking system
  • Network communications codes: “U” codes, having to do with the controller area network wiring bus and its modules

There are further subcategories of codes in these groups:

  • Generic codes: Notated with a “0” as the second digit, which indicates they are common issues for all makes and models of vehicles. These codes are required for a basic diagnosis of the emissions problem.
  • Enhanced or manufacturer specific codes: Notated with a “1” as the second digit, which indicates they are problems that are limited to a specific make or model of vehicle. These codes are considered necessary by vehicle manufacturers, so they could provide a more detailed level of diagnostic information.

Your onboard diagnostic system monitors all of the functions of your vehicle that are related to emissions, which includes fuel and ignition systems, misfires, evaporative emissions controls, catalytic converter and other types of control systems. These functions are typically monitored any time you are driving your car, though some are only monitored under certain operating conditions.

If the system is not operating normally within specific parameters or fails self-tests issued by the onboard diagnostic system, that system will record the diagnostic trouble codes related to the fault, and turn on the check engine light. The check engine light will then remain on until the problem is fixed or the code is cleared.

Remember: this light only tells you some sort of emissions error has occurred—it does not tell you anything about the specific problem that triggered the light to come on, and whether or not that code is serious. Serious problems like overheating or oil pressure loss will not usually turn on the check engine light, but will turn on other warning lights.

For more information about diagnostic codes, contact a mechanic in Lubbock, TX.

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