What it means
Ion current from cylinder 9 is above the expected window. Cross-coupled signal, biased reference, or sensor fault.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The ion-current system reads electrical activity through the cylinder 9 spark plug after the spark to help the ECM assess combustion. This code sets when the cylinder 9 sense signal is above its expected window, potentially because ignition-coil interference, a biased reference, or poor connector contact is distorting it.
Common causes
Most likely first.
- Inductive cross-coupling from ignition coil primary
- Sense reference voltage biased
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Engine misfire or rough running
- Reduced power
How to diagnose it
- Record freeze-frame data and compare live cylinder 9 ion-current and misfire readings with other cylinders to see when the high signal occurs.
- Inspect the cylinder 9 sense-wire routing near the ignition coil for damaged insulation or a route that could pick up coil-primary interference.
- Check the cylinder 9 sense connector for corrosion, loose pins, or high-resistance contact.
- Inspect the cylinder 9 spark plug and coil connections for damage or tracking that may affect the signal.
- Test the cylinder 9 reference and signal circuits for bias, shorts, and unwanted coupling using the wiring diagram and manufacturer's specification.
Common fixes
- Clean and secure corroded or loose cylinder 9 sense connector terminals.
- Repair damaged cylinder 9 wiring and restore the specified routing away from ignition-coil wiring.
- Replace a damaged cylinder 9 spark plug or ignition component if inspection identifies a fault.
- Correct a biased reference or other confirmed cylinder 9 sense-circuit fault.
Can I keep driving?
If the engine runs smoothly and the warning light is steady, limit driving and arrange diagnosis soon because the high cylinder 9 reading may mask combustion problems and emissions may rise. Stop if the engine misfires or loses power, and avoid hard acceleration.
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.