P28B0Cylinder 9 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
- P28B0 marks an electrical circuit fault, usually an interruption, in the ion current measurement of cylinder 9. A ninth cylinder appears only on engines with ten or more cylinders, such as V10, V12 or W12 designs. Ion sensing as a production technique is publicly associated with Saab and Mecel, who brought it into series cars with the Trionic systems on four- and six-cylinder engines; for engines of ten or more cylinders no public application exists, and no manufacturer documents P28B0. The working principle would be unchanged: a small voltage across the idle plug gap, a current only when the hot gas ionises, and an evaluation channel per coil. Without that channel cylinder 9 loses misfire and knock evaluation; checks start at coil 9 and its connector.
- What you may notice
- MIL with ion circuit fault for cylinder 9
- Misfire and knock evaluation of cylinder 9 suspended
- Slight loss of power from retarded timing
- Likely causes
- LikelyCoil 9 connector not latched or with spread terminals
- PossibleIon output of coil 9 without function
- PossibleInterrupted ion line of cylinder 9 in the harness
- 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.