What it means
The ion current signal from cylinder 3 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-sensing system reads electrical current at the cylinder 3 spark plug after combustion so the ECM can judge combustion quality. This code sets when the cylinder 3 signal is present but its range or response does not match the expected pattern, which can result from a worn plug, drifting circuit gain, or an aged sensing element.
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
- Capture freeze-frame data and compare live cylinder 3 ion-sense and misfire readings across idle and the conditions that set the code.
- Inspect the cylinder 3 spark plug for wear or an altered electrode shape, and check its condition against the manufacturer's service guidance.
- Inspect the cylinder 3 ion-sense connector and harness for corrosion, loose pins, damage, or poor routing that could distort the signal.
- Check the signal, reference, and ground circuits for continuity and stable readings, comparing results with the manufacturer's specification.
- If the plug and wiring check out, follow the service procedure to assess ion-sense circuit gain and the sensing element for drift.
Common fixes
- Replace a worn cylinder 3 spark plug with the specified type and gap.
- Clean and secure the cylinder 3 ion-sense connector or repair damaged terminals.
- Repair wiring or reference and ground faults that cause an out-of-range signal.
- Replace a confirmed degraded ion-sense module or sensing element.
Can I keep driving?
If the engine runs smoothly, a short, gentle trip for diagnosis may be reasonable; avoid hard acceleration and heavy loads. Persistent roughness or misfire can worsen and may damage the catalytic converter.
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.