P039C
Cylinder 1 Pressure Variation Low
Generic OBD-II
Common symptoms
What you'll notice
- Check and replace the spark plug in cylinder 1.
- Inspect and clean the fuel injector in cylinder 1.
- Check and replace the ignition coil in cylinder 1.
- Verify and adjust the valve clearance in cylinder 1.
- Perform a compression test on cylinder 1 and repair any issues found.
Common causes
Most likely first
- Faulty or clogged fuel injector for cylinder 1
- Low compression in cylinder 1 due to worn piston rings or valves
- Faulty ignition coil or spark plug for cylinder 1
- Vacuum leak in the intake manifold affecting cylinder 1
- Engine misfire caused by a faulty crankshaft position sensor
How to diagnose & fix
Work through it in order
- Engine misfires or runs rough
- Reduced power or acceleration
- Poor fuel efficiency
- Difficulty starting the engine
- Illuminated check engine light
Read & clear P039C yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.