P28BACylinder 11 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
- P28BA means the cylinder 11 ion reading has fallen below its lower limit. Between sparks a bias voltage sits across the electrodes – 80 V on Saab's T7 – and burning gas lets a current flow that pulls this voltage down in proportion to pressure and temperature. If a fault drains the bias to ground, the evaluator registers the same collapse permanently: a sense wire chafed through, a plug insulator coated with conductive deposits, or water in the boot. Saab's manual notes that a combustion signal shorted to ground produced no dedicated code there, only misfire codes, so a separate low-signal code is a later refinement. No manufacturer documents P28BA, and no ion-sensing twelve-cylinder engine is publicly known. P28BB is the high-side fault, P28B8 the open circuit.
- What you may notice
- MIL on with a low ion signal stored for cylinder 11
- Misfire code P0311 possible although the engine runs smoothly
- Power slightly reduced by conservative timing
- Likely causes
- LikelyIon signal wire of cylinder 11 chafed and touching ground
- PossibleConductive deposits on the cylinder 11 plug insulator
- PossibleMoisture or a carbon track in the cylinder 11 plug boot
- RareBias voltage generation in coil 11 failed
- 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 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.