P28AECylinder 8 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
- P28AE stands for an ion reading from cylinder 8 that stays too low or near zero. Either the measuring voltage never reaches the plug, because the coil's bias stage or its supply has failed, or it drains away to ground through a damaged signal wire, a wet plug well or a tracked boot. With ion sensing the plug doubles as knock and combustion sensor, so a dead reading also takes knock protection for cylinder 8 away and the engine computer tends to fall back on retarded timing. A supply fault affecting the whole module would rather appear as P28C0 to P28C2 than as a single-cylinder code. No manufacturer documents P28AE in public; an eight-cylinder ion-sensing engine is not described. P28AF is the high-side fault.
- What you may notice
- MIL lit with a low ion reading for cylinder 8
- Knock protection of cylinder 8 lost, timing retarded
- Possible misfire report for cylinder 8
- Likely causes
- LikelyWater or oil in the cylinder 8 plug well
- PossibleDamaged cylinder 8 signal wire shorted to ground
- PossibleBias stage of coil 8 not producing measuring voltage
- 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 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.