What you'll be able to do after this Course: read your car's trouble codes yourself, understand what they do and don't tell you, fix the handful of causes that are genuinely DIY (a loose gas cap, a misfiring coil or plug, a dirty sensor), confirm the fix, and get the car ready to pass an emissions inspection.
Every car and light truck sold in the United States since the 1996 model year (1997 for diesels) has a second-generation on-board diagnostic system, OBD II [1]. It watches the engine and emissions systems, and when something is out of range it stores a code and turns on the check engine light. Reading that code takes a $20 tool or a free scan at a parts store. Understanding it is where people go wrong.
The one idea that saves you money
A code tells you what the computer saw, not what part failed. "P0171, system too lean" means the engine is getting more air than fuel. That could be a vacuum leak, a dirty airflow sensor, a weak fuel pump, a clogged injector or an exhaust leak ahead of the oxygen sensor. Replacing the part named most often online is how people spend $300 and keep the light. This Course teaches you to narrow it down first.
How long it takes
| Stage | Time |
|---|---|
| Read codes and freeze frame | 10 minutes |
| Research the code for your exact car | 20–40 minutes |
| Simple DIY tests (Chapter 7) | 15–60 minutes |
| Confirming the fix and readiness (Chapters 10–11) | A few days of normal driving |
These are AlongSide's estimates.