Learn what OBD2 codes mean, how to scan them, and what to do next when the check engine light appears—without panic or guesswork.
First: flashing vs. solid check engine light
- Flashing: often indicates a severe misfire that can damage the catalytic converter—reduce load and get it checked ASAP.
- Solid: usually less urgent, but still needs diagnosis.
What an OBD2 code really is
Codes are a starting point—not a verdict. Example: P0420 doesn’t mean “replace the catalytic converter.” It means the system detected efficiency below threshold, which can be caused by leaks, sensors, misfires, fuel issues, or the cat itself.
The 5-step plan
1) Scan codes + freeze-frame
Freeze-frame tells you the conditions when the fault happened (RPM, temp, load).
2) Check for simple issues first
Loose gas cap? obvious cracked hose? disconnected sensor after recent work?
3) Look for patterns
Multiple codes together often point to one root cause (vacuum leak, low voltage, etc.).
4) Clear codes only after you document them
Clearing without notes makes diagnosis harder.
5) Use a guided diagnostic plan
This is where AI helps: it can turn “codes + symptoms” into “test these 3 things first.”
Call to action
If you have codes but don’t know what to test next, start a free WrenchWizardAI diagnosis and get a prioritized checklist you can follow.