P03BC
Cylinder 4 Combustion Performance
Generic OBD-II
Common symptoms
What you'll notice
- Replace spark plugs in cylinder 4
- Check and replace ignition coil in cylinder 4
- Inspect and clean fuel injectors in cylinder 4
- Perform compression test on cylinder 4 and repair any issues found
- Conduct a thorough inspection of the cylinder 4 fuel delivery system and fix any faults or leaks.
Common causes
Most likely first
- Faulty spark plug or ignition coil in cylinder 4
- Clogged or dirty fuel injector in cylinder 4
- Low compression in cylinder 4 due to worn piston rings or valves
- Vacuum leak in the intake manifold near cylinder 4
- Faulty oxygen sensor in cylinder 4's exhaust system
How to diagnose & fix
Work through it in order
- Misfires in cylinder 4
- Engine hesitation or lack of power
- Rough idling or vibrations
- Decreased fuel efficiency
- Check Engine Light (CEL) illuminates
Read & clear P03BC yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.