For years vehicle manufacturers have fitted on-board diagnostic (OBD) systems that provide codes to help identify specific issues. You can find the most recent diesel powertrain codes for Duramax, Powerstroke, and Cummins in the right column of this blog. (See the button Diesel Technical Bulletins.)
But what are these systems and what do these codes mean? Put simply, an OBD system, or on-board diagnostic system, is an on-board computer fitted to your diesel engine that monitors the performance of your truck, including its powertrain, ignition, gearbox and emissions system.
When the truck’s on-board diagnostics system identifies a problem with the vehicle’s performance, it turns on a dashboard warning light and registers a code that identifies the issue.
This engine code, called a Diagnostic Trouble Code (DTC), is stored in the OBD-II system and can only be accessed by connecting a scan, or diagnostic tool into the OBD-II diagnostic socket and reading the DTC off the display of the scanner.
This light is to let you know that a possible fault has developed in the engine management system or another function and may require attention. When you see this appear, check your handbook for instructions on what action to take for your make and model of vehicle.
Diagnostic Trouble Codes, also known as engine fault codes, are five-digit codes that identify a particular problem in the car. These codes are displayed on the scanning tool when it’s connected to the OBD system.
The five-digit DTC includes one letter usually followed by four numbers (e.g. P1234). Each individual combination of letters and numbers relates to a specific problem within the car, whether a generic issue or a manufacturer-specific error.
A DTC won’t tell you which specific part of your car needs fixing or replacing, but it will tell you -- or your mechanic -- what you need to test in order to diagnose the issue. Within the five-digit DTC, one of four letters (P, B, C, U) always comes first and relates to the part of the car that has the issue: P - powertrain, B - body, C - chassis, and U - network.
The second digit (either 0 or 1) relates to whether it’s a general issue (0) or a manufacturer specific problem (1), while the third corresponds to the specific system with the issue, such as the ignition, and can be either a number or letter. The final two digits are numbers that relate to the specific fault description, and there is no pre-approved key to help decode these final two digits.
“May the Force be with you,” --Obi-Wan Kenobi, the Jedi Master.
