What it means
Ion current from cylinder 1 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 ECM monitors ion current from cylinder 1 through its spark-plug sensing path to assess combustion after ignition. This code sets when the cylinder 1 signal is above the expected range, which can result from ignition interference, a biased reference, or a sensing fault.
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 counts for cylinder 1, noting whether the fault occurs during ignition events or under particular engine loads.
- Inspect cylinder 1 ion-sense wiring and connectors for corrosion, loose pins, damaged insulation, or routing close to ignition-coil primary wiring.
- Check the cylinder 1 spark plug and ignition components for damage or incorrect installation that could contribute to signal interference.
- Using the manufacturer's wiring diagram, test the cylinder 1 sense circuit and reference for unwanted bias or cross-coupling with ignition wiring.
- If wiring and connections are sound, test the cylinder 1 ion-sense component and module according to the manufacturer's procedure.
Common fixes
- Reroute or secure cylinder 1 sense wiring as specified to reduce ignition-coil interference.
- Repair corroded, loose, or damaged terminals in the cylinder 1 sensing connector.
- Correct a biased reference or wiring fault in the cylinder 1 ion-sense circuit.
- Replace the failed ion-sense component or module if testing confirms it.
Can I keep driving?
If the engine runs smoothly, limit driving and arrange diagnosis soon because unreliable combustion monitoring can accompany a misfire and lead to catalytic-converter damage. Stop driving if it misfires severely, loses power, or the warning light flashes.
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.