What it means
The ECU compares each cylinder's contribution to crankshaft speed (rough run analysis) and determined cylinder 3 contributes less or more than the average. This points to a mechanical or fuel delivery problem rather than a pure ignition fault.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module estimates each cylinder's contribution by tracking small changes in crankshaft speed. This code means cylinder 3 contributes differently from the others, commonly because its injector is restricted or worn or because cylinder 3 has low compression.
Common causes
Most likely first.
- Injector clogged or worn
- Low compression on cylinder
Symptoms
- Check-engine light
- Rough idle or engine vibration
- Reduced power
- Engine misfire
How to diagnose it
- Review freeze-frame data, cylinder 3 misfire counts, and any available injector balance or rough-running data to see when its contribution falls behind.
- Inspect the cylinder 3 injector connector and wiring, and check for intake or exhaust leaks near that cylinder.
- Compare cylinder 3 injector operation or balance with the other cylinders using a scan tool and the specified test method.
- If injector operation is suspect, check cylinder 3 fuel delivery and injector condition against the manufacturer's specification.
- If fuel delivery is satisfactory, perform a compression test on cylinder 3 and compare it with the other cylinders and the manufacturer's specification.
Common fixes
- Repair a loose or damaged cylinder 3 injector connection or wiring found during inspection.
- Clean or replace a restricted or worn cylinder 3 injector if testing confirms poor delivery.
- Repair a leak affecting cylinder 3 if inspection identifies one.
- Repair the mechanical cause if cylinder 3 compression is below specification.
Can I keep driving?
A brief, gentle drive may be possible if the engine is stable, but avoid heavy loads and prolonged driving while cylinder 3 is misfiring. Stop if vibration becomes severe or power drops sharply; continued misfire can damage the catalytic converter.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.