Understanding the Most Common OBD2 Trouble Codes and What They Mean

When the check engine light comes on, the first step is understanding what the trouble code means. Some OBD2 codes appear far more frequently than others, and recognizing them can help you diagnose issues quickly — especially with a reliable tool like the CHEPQ OBD2 scanner.

Below are the most common OBD2 codes and what each one usually indicates.

1. P0300 — Random/Multiple Cylinder Misfire

This code means the engine is misfiring but can’t pinpoint one specific cylinder.Possible causes:

• Bad spark plugs

• Faulty ignition coils

• Fuel delivery issues

• Vacuum leaks

CHEPQ scanners can help identify which cylinder is misfiring and why.

2. P0420 — Catalyst System Efficiency Below Threshold

This code suggests your catalytic converter isn’t performing correctly.Common causes include:

• Aging catalytic converter

• Faulty oxygen sensors

• Exhaust leaks

Ignoring this code can lead to expensive repairs.

3. P0171 — System Too Lean (Bank 1)

This means the engine is receiving too much air or too little fuel.Often caused by:

• Dirty MAF sensor

• Vacuum leaks

• Weak fuel pump

• Clogged injectors

CHEPQ’s live data helps pinpoint the airflow or fuel issue.

4. P0442 — EVAP System Leak Detected

This code indicates a small fuel vapor leak.Usually caused by:

• Loose gas cap

• Faulty purge valve

• EVAP hose cracks

It’s one of the most common — and often easiest — issues to fix.

5. P0507 — Idle Control System RPM Too High

This points to an air intake or throttle body issue.Common triggers:

• Dirty throttle body

• Intake air leaks

• Improper idle control

Live data monitoring helps spot irregular RPM behavior.

Conclusion

Knowing common OBD2 trouble codes saves time, reduces repair costs, and improves vehicle health. With CHEPQ’s diagnostic tools, understanding and resolving these issues becomes faster, simpler, and far more accurate.