Diagnose before you replace parts.
A trouble code is a clue—not automatically the failed part. Use a logical process to test the system.
Check Engine Light
Start with codes, freeze-frame data, symptoms and basic visual checks.
Misfires
Separate ignition, fuel, air and mechanical causes before buying parts.
No-Start
Check battery/cranking, fuel, spark, compression and engine timing systematically.
Vacuum Leaks
Use fuel trims, visual inspection, listening and appropriate leak-testing methods.
Electrical Problems
Learn basic voltage, resistance, continuity and voltage-drop testing.
OBD-II Codes
Understand what common P-codes mean and what they do—and don't—prove.
Need a basic OBD-II scanner?
The FOXWELL NT301 can be a practical option for reading engine codes and viewing live data. Always verify that the tool supports the functions you need for your exact vehicle.
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