P2891Cylinder 1 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
- Here the ion signal of cylinder 1 is present but implausible: its level or waveform does not fit engine speed and load, or it differs clearly from the other cylinders. Fouled or worn spark plugs are a frequent reason, since soot or oil deposits form a leakage path that distorts the small measuring current; a cracked insulator or water in the plug well has a similar effect. In Saab's later processing module (9-3 from 2009), cylinder 1 enters on its own ion input and is combined with cylinder 3 in a combustion signal used for synchronisation and misfire detection, so a distorted cylinder 1 signal affects that pair. No manufacturer documents P2891 publicly. Electrical opens and shorts are covered by P2890, P2892 and P2893.
- What you may notice
- MIL, sometimes together with misfire codes
- Rough idle or hesitation
- Reduced power due to cautious knock control
- Likely causes
- LikelySooted, oil-fouled or worn spark plug in cylinder 1
- PossibleMoisture or oil in the plug well of cylinder 1
- PossibleIon measuring stage of coil 1 drifting
- RareReal combustion fault in cylinder 1 (mixture, compression)
- 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 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.