P28B1Cylinder 9 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
- P28B1 indicates that cylinder 9 produces an ion signal of believable electrical level whose shape or strength does not match engine speed, load or the neighbouring cylinders. Since the reading reflects combustion pressure and temperature, the root cause is often mechanical or mixture-related: a worn or oil-fouled plug, a leaking valve, a weak injector on cylinder 9, or condensation in the plug well. Saab used the same signal to count missing combustions per cylinder over 1000 crankshaft revolutions, the interval CARB also prescribes for emission-relevant misfire. No manufacturer documents P28B1, and engines with nine or more cylinders using ion sensing are not publicly described. P28B0, P28B2 and P28B3 are the electrical faults; P0309 may follow.
- What you may notice
- MIL, possibly with misfire code P0309
- Noticeably uneven running at idle
- Higher fuel consumption
- Likely causes
- LikelyWorn or oil-fouled spark plug in cylinder 9
- PossibleWeak spray from the cylinder 9 injector
- RareLeaking valve on cylinder 9
- RareCondensation in the cylinder 9 plug well
- 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 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.