P28ACCylinder 8 Ion Current Sense Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28AC flags a general electrical fault in the ion current path of cylinder 8, typically an open connection, so no usable signal reaches the evaluation electronics. On a V8 this is the highest-numbered cylinder, on V10 and V12 engines a middle one; which bank it sits on depends on the maker's numbering. A cylinder-specific code presumes one input per coil, as in the CDM of Saab's later Trionic T8, which receives a separate ion line from each of the four coils. Older T7 modules merged cylinders into shared detectors and could not name a single one. No manufacturer documents P28AC, and no eight-cylinder ion-sensing engine is publicly known. Check coil 8, its plug, connector and wiring first; range and level faults are P28AD, P28AE and P28AF.
- What you may notice
- MIL with a circuit fault stored for cylinder 8
- No misfire or knock assessment for cylinder 8
- Engine may run with conservative timing and lower power
- Likely causes
- LikelyLoose or corroded connector in the cylinder 8 ion line
- PossibleMeasuring stage of coil 8 failed
- PossibleBroken conductor between coil 8 and the evaluation module
- RareCylinder 8 input of the evaluation module defective
- 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: €50 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.