Diagnostics & Engine

Diagnostics & Engine answers from Piston Journal: troubleshooting fixes, step-by-step how-tos, comparisons and quick facts, each with the short answer first.

Diagnostics & Engine

Can a OBD2 Scanner Clear Codes? What Really Gets Erased

Can a OBD2 scanner clear codes? Yes, but it also wipes freeze frame data and resets readiness monitors, and permanent codes stay until the fault is fixed.

Diagnostics & Engine

OBD2 Not Ready Smog Check: Why It Fails and How to Fix It

OBD2 not ready smog check failures mean readiness monitors haven't finished their self-tests. Why that happens, how to set them, and what California allows.

Diagnostics & Engine

Spark Plugs vs Fuel Injectors: Which Causes Your Misfire?

Spark plugs vs fuel injectors: plugs light the mixture, injectors meter fuel. How to tell which one is behind a misfire or rough idle, and which to check first.

Diagnostics & Engine

Why Is My OBD2 Port Not Communicating? 7 Causes and Fixes

Why is my OBD2 port not communicating? Usually the ignition is off, a fuse has blown, the battery is weak or the plug is damaged. Step-by-step checks inside.