P28ABCylinder 7 Ion Current Sense Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28AB is set when the cylinder 7 ion signal sits above the highest value a healthy measuring circuit can deliver. Typical triggers are a signal lead touching a supply wire, moisture bridging the coil connector, or a coil whose ignition pulse bleeds into its measuring output. A constant high reading is treacherous for diagnosis because it can look like permanent combustion and so mask real misfire. Saab's T7 V6 shows comparable logic only per bank: its codes P1313 and P1324 flag a combustion line stuck above 5 V for 200 firings. No manufacturer publishes P28AB, and a V8 or larger engine using ion sensing is not publicly described. The low-side counterpart is P28AA; P28A9 handles readings that are in range but implausible.
- What you may notice
- MIL lit with a high ion reading stored for cylinder 7
- Genuine misfire on cylinder 7 may go unreported
- Timing pulled back on cylinder 7, slightly less power
- Likely causes
- LikelyIon signal lead of cylinder 7 touching a supply wire
- PossibleMoisture bridging contacts in the coil 7 connector
- RareCoil 7 leaking its ignition pulse into the measuring output
- 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: €40 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.