What it means
Ion current from cylinder 1 is below the expected window. Spark plug fouled, signal wire shorted to ground, or sensing path interrupted.
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 below the expected range, which can result from a fouled plug, a grounded signal wire, or a poor connection.
Common causes
Most likely first.
- Spark plug fouled with carbon or oil
- Sense wire shorted to ground
- 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 to see when its low signal occurs.
- Inspect the cylinder 1 spark plug for carbon or oil fouling and check for visible damage that could weaken the sensing signal.
- Inspect the cylinder 1 ion-sense wire and connector for a short to ground, damaged insulation, corrosion, or loose terminals.
- With the circuit isolated as specified by the manufacturer, test the cylinder 1 signal wire for shorts to ground and check connector contact quality.
- If the plug and wiring pass, test the cylinder 1 ion-sense path and module according to the manufacturer's procedure.
Common fixes
- Replace a carbon- or oil-fouled cylinder 1 spark plug with the specified type.
- Repair a cylinder 1 ion-sense wire that is shorted to ground.
- Clean or repair corroded or loose terminals in the cylinder 1 sensing connector.
- Replace a failed ion-sense component if circuit testing confirms it.
Can I keep driving?
Avoid extended driving if cylinder 1 is misfiring, since unburned fuel can overheat and damage the catalytic converter. Stop if the engine shakes 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.