How we write the field guides
Check Engine Light Code explains what an OBD-II scan recorded and what information to gather next.
Where the information comes from
We use manufacturer documents for vehicle-specific examples, EPA material for OBD background and state program references for inspection details. Each code guide links its sources. Bulletin coverage depends on the vehicle and sometimes the VIN or software.
What a code can tell you
The scan shows what a module observed. The freeze frame, related codes, vehicle details and diagnostic tests help you work out the cause. Follow the vehicle owner’s manual for roadside instructions.
What this edition covers
The library currently focuses on selected generic codes and US light-duty OBD-II. Read the code-format guide if your tool shows an enhanced code or suffix.
Read the OBD-II code formatHow pages are checked
Every page shows the date its sources were last checked against the original documents. An independent automotive technician review of the diagnostic advice is still in progress, and each page says so until its review is complete. When a reviewer signs off, the page will name the reviewer, their qualifications and the review date.
Vehicle-specific examples
Many pages include an example from a manufacturer bulletin or owner’s manual. Those examples apply to the vehicles the document covers, often limited by model year, engine or VIN range. We say which vehicles a document covers, and keep it separate from advice that applies broadly.
Corrections
If you find an error, tell us. We log every correction with the date and what changed. See the corrections policy and log