P28B9Cylinder 11 Ion Current Sense Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P28B9 stands for an ion signal from cylinder 11 whose voltage stays inside the valid band but whose behaviour makes no sense: too weak or too strong for the current speed and load, or out of line with the other eleven cylinders. Such rationality tests belong to the input-component monitoring CARB demands. Since the reading follows the heat and pressure of the burning charge, the trigger is frequently in the cylinder itself, such as a worn or oil-fouled plug, a weak injector or a leaking valve. Saab's T7 V6 shows how strict this gets: it tallied missing combustions per cylinder and compared them with an allowance taken from a speed and load table, enabled only above 72 kPa ambient pressure and -7 °C. No manufacturer documents P28B9. P28B8, P28BA and P28BB are the electrical faults.
- What you may notice
- MIL on after the fault is confirmed on a second trip
- Slightly rough running, sometimes with misfire code P0311
- Unsteady ignition timing on cylinder 11
- Likely causes
- LikelyWorn or oil-fouled spark plug on cylinder 11
- PossibleCylinder 11 injector delivering too little or spraying poorly
- RareLow compression on cylinder 11 (valve or ring leakage)
- RareWater or oil standing in the plug well of cylinder 11
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.