Connecting an OBD2 scanner beneath a modern dashboard

Free diagnostic library

Fault Code Guides

Understand the code, test the inexpensive causes first, and make the repair with evidence.
Check Engine Light On? Do These 5 Things First (Before the Shop)
A check engine light doesn't have to mean a big bill. These 5 steps tell you in minutes whether it's a $5 fix, a safe-to-drive issue, or something urgent. Read more...
How to Use an OBD2 Scanner: Beginner's Guide (No Mechanic Needed)
Plug in, read the code, understand it, fix the cheap cause first. The complete beginner's guide to using an OBD2 scanner on any car from 1996 onwards. Read more...
P0171 System Too Lean: The $20 Fix Most People Miss
P0171 means too much air or too little fuel on bank 1. Nine times out of ten the fix is a dirty MAF sensor or a cracked vacuum hose – not an expensive part. Read more...
P0300 Random Misfire: Diagnose It in 15 Minutes Without a Mechanic
P0300 means multiple cylinders are misfiring randomly. Here's the 15-minute driveway diagnosis that finds the cause – usually a $10–$60 part. Read more...
P0420 Code: What It Means, What Causes It, and the Cheapest Fix First
P0420 means your catalytic converter efficiency is below threshold – but the cat itself is only sometimes the culprit. Check these cheap causes first before spending $1,000+. Read more...