What it means
The ion current signal from cylinder 8 is outside the expected range for combustion conditions. Combustion quality cannot be assessed reliably.
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 evaluates combustion in cylinder 8 by measuring electrical activity through its spark plug after the spark. This code sets when the cylinder 8 signal is present but falls outside the expected range or performance pattern, so the ECM cannot assess combustion reliably.
Common causes
Most likely first.
- Spark plug aged - electrode shape changed
- Ion sense circuit gain drift
- Sensor element aged beyond calibration window
Symptoms
- Check-engine light on
- Rough idle or engine misfire
- Reduced engine performance
How to diagnose it
- Record freeze-frame data and compare live cylinder 8 ion-current and misfire data with other cylinders under the same operating conditions.
- Inspect the cylinder 8 spark plug for electrode wear, deposits, oil fouling, or damage that could change its sensing behaviour.
- Check the cylinder 8 sense-circuit connector and wiring for loose or corroded terminals, damage, or poor contact.
- Check for other ignition or combustion faults affecting cylinder 8 that could make its ion-current reading differ from the expected pattern.
- If the plug and wiring are sound, test the cylinder 8 sense circuit and module response according to the vehicle wiring diagram and manufacturer's specification.
Common fixes
- Replace a worn or fouled cylinder 8 spark plug with the specified type.
- Clean and secure poor cylinder 8 sense-circuit connector contacts.
- Repair damaged cylinder 8 sense wiring or connector terminals.
- Replace or recalibrate a faulty ion-sense component only after testing confirms gain drift or an out-of-calibration sensor.
Can I keep driving?
If the engine runs normally and the warning light is steady, drive gently and have the cylinder 8 signal checked soon because combustion monitoring may be unreliable and emissions may rise. Stop if a misfire develops or power drops.
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.