What it means
The control module detected that cylinder 9 is not contributing to engine power as expected. Possible causes include an injector, compression, or other cylinder-specific problem.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The control module evaluates how much cylinder 9 contributes to engine output, using engine speed changes and, depending on the vehicle, other operating data. It sets this code when cylinder 9 contributes less than expected; an injector restriction, ignition fault, low compression, or wiring problem can be responsible.
Common causes
Most likely first.
- Cylinder 9 injector restricted or faulty
- Cylinder 9 ignition coil or spark plug fault
- Low compression on cylinder 9
- Wiring or connector fault
Symptoms
- Check-engine light
- Rough idle or engine vibration
- Reduced power
- Engine misfire
How to diagnose it
- Save the freeze-frame data and review live misfire counts or cylinder contribution data to confirm that cylinder 9 is the weak cylinder and note when it happens.
- Inspect cylinder 9 ignition components, injector connector, and nearby wiring for damage, poor connections, or signs of fuel or oil contamination.
- Check the cylinder 9 spark plug and ignition coil using the vehicle's diagnostic procedure, comparing with another cylinder only where the manufacturer permits.
- Test cylinder 9 injector operation and its wiring; use the manufacturer's procedure to distinguish an electrical fault from restricted fuel delivery.
- If ignition, injector, and wiring checks do not explain the low contribution, perform a compression or leak-down test on cylinder 9 and compare with the manufacturer's specification.
Common fixes
- Repair a loose or damaged cylinder 9 connector or wiring fault.
- Replace a confirmed faulty cylinder 9 spark plug or ignition coil.
- Clean or replace the cylinder 9 injector if testing confirms restricted or faulty operation.
- Repair the cylinder 9 mechanical fault identified by compression or leak-down testing.
Can I keep driving?
A mild rough idle with a steady warning light may allow a short, gentle trip for diagnosis, but avoid heavy loads because cylinder 9 is not contributing normally. If the light flashes, vibration is severe, or power falls substantially, stop driving to reduce the risk of catalyst or engine damage.
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.