OBD-II Diagnostic Trouble Codes
On-Board Diagnostics II (OBD-II) is the standard diagnostic system for all light-duty vehicles sold in the US since 1996 and most medium/heavy-duty vehicles.
Code Ranges
Engine, transmission, and drivetrain codes defined by SAE. Common in roadside inspections.
OEM-specific engine and transmission codes. Interpretation varies by manufacturer.
Additional SAE-defined powertrain codes introduced in later OBD-II revisions.
Mixed SAE and OEM powertrain codes.
Airbags, seatbelts, HVAC, instrument cluster. Less common in CMV inspections.
ABS, traction control, stability systems. Relevant to brake inspections.
CAN bus, module communication faults. Can indicate wiring or ECU issues.
Reading OBD-II Codes
Each OBD-II code follows the format Xnnnn where X is the system letter (P/B/C/U) and nnnn is the numeric identifier.
During FMCSA Level I and II inspections, inspectors may scan for active fault codes using OBD-II readers. Codes related to emissions, brakes, or lighting systems can result in violations under FMCSR Part 393.
To look up a specific code, use the search bar or navigate to /codes/OBD2/{code}/.