P28B2Cylinder 9 Ion Current Sense Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28B2 is stored when the ion current measured at cylinder 9 remains under its lower plausibility limit. In an ion-sensing ignition each coil both fires the plug and supplies the measuring voltage, so a coil 9 with a weak bias stage, a cracked plug insulator or a signal wire grounded in the harness all reduce the current reaching the evaluator. Because the evaluation can hardly tell a dead circuit from a cylinder that does not burn, misfire code P0309 frequently accompanies it. On Saab's four-cylinder T7, a ground short on a combustion line triggered no special code at all, only misfire reports. No manufacturer publicly documents P28B2, and no ion-sensing V10 is known. P28B3 is the high fault, P28B1 the plausibility fault.
- What you may notice
- MIL with low ion reading on cylinder 9
- P0309 often stored at the same time
- Reduced power under load
- Likely causes
- LikelyCylinder 9 signal wire grounded in the harness
- PossibleCracked insulator on the cylinder 9 plug
- PossibleCoil 9 with weak bias stage
- 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: €30 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.