What it means
Ion current from cylinder 3 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 cylinder 3 spark plug to detect current in the gases after combustion, giving the ECM information about that cylinder's burn. This code sets when the cylinder 3 sense signal rises above its expected range; ignition-coil interference, a biased reference, or a poor connector contact can cause the high 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
- Save freeze-frame data and review live cylinder 3 ion-sense and misfire readings to see under what conditions the signal rises too high.
- Inspect the cylinder 3 plug, connector, and harness for corrosion, loose pins, damaged insulation, or sense wiring routed close to ignition-coil wiring.
- Check connector terminal fit and sense-wire continuity for excessive contact resistance or unintended connection to another circuit.
- Measure the cylinder 3 ion-sense reference and signal circuits during the fault and compare them with the manufacturer's specification.
- If the circuit checks pass, investigate ignition-coil interference and test the ion-sense module using the manufacturer's procedure.
Common fixes
- Clean and secure the cylinder 3 ion-sense connector or repair corroded terminals.
- Repair damaged wiring and correct harness routing as specified for the vehicle.
- Correct a biased reference or other circuit fault causing the high signal.
- Replace a confirmed faulty ion-sense module or sensing component.
Can I keep driving?
If the engine runs smoothly, a short, gentle trip to diagnosis may be reasonable; avoid hard acceleration and heavy loads. Stop driving if it develops a strong misfire, as continued misfiring can 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.