P289C
Cylinder 4 Ion Current Sense Circuit
The ECM cannot read a valid ion current signal from cylinder 4. Ion current sensing relies on the spark plug acting as an electrode after combustion.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Ion sense module failedCommon
- Wiring or connector faultPossible
Parts involved
- Spark Plug Cyl 4
- Ignition Coil Cyl 4
- Ion Sense Module
P289C is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.