What it means
The ECU compares each cylinder's contribution to crankshaft speed (rough run analysis) and determined cylinder 4 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 detecting changes in crankshaft speed during combustion. P0272 means cylinder 4 contributes differently from the others, pointing to a cylinder-specific fueling or mechanical issue rather than identifying one failed part.
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
- Save freeze-frame data and check live misfire counts or cylinder-balance data to confirm that cylinder 4 is the outlier.
- Inspect cylinder 4's injector connector and wiring, then check for obvious intake or fuel-delivery issues affecting that cylinder.
- Test the cylinder 4 injector's electrical operation and compare its delivery or balance with other cylinders using the vehicle's specified procedure.
- Check cylinder 4 compression and compare it with the other cylinders and the manufacturer's specification.
- If compression and injector checks do not explain the imbalance, inspect cylinder 4 valvetrain and related mechanical components.
Common fixes
- Repair a loose, corroded, or damaged cylinder 4 injector connection.
- Clean or replace a restricted or faulty cylinder 4 injector after confirming the fault.
- Repair a cylinder 4 mechanical problem identified by compression or valvetrain checks.
- Address any other verified cylinder 4 fuel-delivery fault found during testing.
Can I keep driving?
Avoid hard acceleration if the engine vibrates or misfires; continued misfiring can damage the catalytic converter. Stop if the engine runs severely rough or loses significant power, since a mechanical fault may worsen with continued use.
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.