P28BFCylinder 12 Ion Current Sense Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28BF signals that the cylinder 12 ion input sits above its permitted window. A sense wire touching a powered conductor, moisture bridging pins in the coil 12 connector or spark energy escaping inside the coil can all push it there. The consequence is easiest to see on Saab's T7 V6, where knock was read from the ion flow: a signal above the knock level made the engine computer retard that cylinder step by step, and if average retard across all cylinders grew too large it enriched the mixture and finally limited air mass. A false high reading can therefore cost power and fuel. Engine computers are expected to reject such a value and fall back to safe timing. No manufacturer documents P28BF publicly. P28BE is the low-side fault, P28C2 an overvoltage of the module supply.
- What you may notice
- Stored high ion signal code for cylinder 12, MIL depending on the maker
- Noticeably less power from heavy timing retard
- Higher fuel consumption from protective enrichment
- Likely causes
- LikelySense wire of cylinder 12 touching a powered conductor
- PossibleMoisture bridging pins in the coil 12 connector
- RareInternal flashover in coil 12 reaching the measuring path
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.