What it means
Ion current from cylinder 2 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-sensing system uses the spark plug in cylinder 2 to detect electrical current in the gases after combustion, helping the ECM assess the burn. This code sets when the cylinder 2 sense signal is higher than the module expects, which can happen if ignition-coil interference couples into the signal, the reference is biased, or a poor connector contact distorts the reading.
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 on
- Rough idle or engine misfire
- Reduced engine performance
How to diagnose it
- Record freeze-frame data and check live misfire or ion-sense data to see when cylinder 2's signal becomes high and whether the symptom occurs under load or at idle.
- Inspect the cylinder 2 spark plug, ion-sense connector, and harness for contamination, corrosion, loose pins, chafing, or routing close to ignition-coil wiring.
- Check the cylinder 2 connector terminals and sense-wire continuity for excessive contact resistance or an unintended connection to another circuit, following the wiring diagram.
- Measure the ion-sense reference and signal circuit while the fault is present and compare readings with the manufacturer's specification.
- If wiring and reference checks pass, test for coil-primary interference and evaluate the ion-sense module using the vehicle's service procedure.
Common fixes
- Clean and secure the cylinder 2 ion-sense connector or repair corroded terminals.
- Repair damaged cylinder 2 sense wiring and restore separation from ignition-coil wiring as specified.
- Correct a biased ion-sense reference circuit fault.
- Replace a confirmed faulty ion-sense module or other failed component.
Can I keep driving?
If the engine runs smoothly, a short, gentle trip to diagnosis may be reasonable, but avoid hard acceleration and heavy loads. A rough-running misfire can worsen and may damage the catalytic converter; stop driving if the misfire becomes severe.
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.