P28A3
Cylinder 5 Ion Current Sense Circuit High
Ion current from cylinder 5 is above the expected window. Cross-coupled signal, biased reference, or sensor fault.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Inductive cross-coupling from ignition coil primaryCommon
- Sense reference voltage biasedPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Spark Plug Cyl 5
- Ignition Coil Cyl 5
- Ion Sense Module
P28A3 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.