P28A9Cylinder 7 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
- P28A9 means cylinder 7 returns an ion signal that is electrically sound but not believable for the current speed and load, or that stands out against the other cylinders of an eight-or-more-cylinder engine. Because the current through the plug gap grows with combustion pressure and temperature, a lean or misfiring cylinder 7 produces this picture as readily as a fouled plug or moisture in the well. The signal serves both misfire detection and knock control, as Saab's ion-sensing T7 V6 illustrates by analysing each bank's ion flow for knock. No manufacturer documents P28A9 publicly, and no production V8 with this measurement is publicly described. Electrical faults on cylinder 7 are reported as P28A8, P28AA and P28AB.
- What you may notice
- MIL, possibly together with P0307
- Uneven idle
- Knock control retards timing more often
- Likely causes
- LikelyFouled or worn spark plug in cylinder 7
- PossibleLean mixture or misfire in cylinder 7
- RareMoisture in the plug well of cylinder 7
- 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 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.