Ignition coil A (cylinder 1 on many engines) circuit fault — misfire likely.
Common symptoms
- Misfire
- Rough idle
- P0301 often sets with this code
Typical causes
- Failed coil-on-plug
- Bad spark plug breaking down
- Primary/secondary wiring open
- Moisture in connector
What scanner do you need?
Basic OBD2 code reader (engine codes, live data, smog readiness)
Use live data and freeze frame to confirm the fault before replacing parts. ABS, SRS, and network U-codes usually require a full-system scanner.
Diagnostic tips
- Record freeze frame data when the code first sets
- Clear the code only after fixing the root cause
- Check for related pending codes that point to a common issue
- Verify battery voltage is above 12.4V before chasing sensor codes