What it means
The ion current signal from cylinder 5 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
After the spark, the engine control module (ECM) uses ion current at cylinder 5's spark plug to assess combustion. This code sets when the signal is present but falls outside the expected range for cylinder 5 under the recorded operating conditions.
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
- Read freeze-frame data and live misfire or ion-sense readings to see when cylinder 5's signal goes out of range and whether other cylinders are affected.
- Inspect cylinder 5's spark plug for an eroded or altered electrode, deposits, oil, or damage that could change its sensing behavior.
- Check the cylinder 5 ion-sense wiring and connectors for loose pins, corrosion, heat damage, or routing close to ignition-coil wiring.
- Compare cylinder 5's signal with other cylinders under similar conditions to distinguish a cylinder-specific issue from a shared supply or reference problem.
- Test the cylinder 5 sensing path, reference, and module gain against the manufacturer's specification before replacing the ion-sense module or sensor.
Common fixes
- Replace an aged or damaged cylinder 5 spark plug with the specified type.
- Clean and secure corroded or loose cylinder 5 ion-sense connector contacts.
- Repair damaged or poorly routed cylinder 5 ion-sense wiring.
- Replace a faulty ion-sense element or module if circuit tests confirm gain drift or a failed sensor.
Can I keep driving?
If the engine runs smoothly, limit driving and avoid hard acceleration until diagnosed; unreliable cylinder 5 combustion monitoring can allow a misfire to go unnoticed and increase emissions. Stop driving if it misfires severely or loses power.
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.