P2891 code meaning
Cylinder 1 Ion Current Sense Circuit Range/Performance
Powertrain system Generic code P28xx codes Check engine light
What P2891 means
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.
P2891 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P2891
- MIL, sometimes together with misfire codes
- Rough idle or hesitation
- Reduced power due to cautious knock control
Common causes of P2891
- Most 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
- Less likelyReal combustion fault in cylinder 1 (mixture, compression)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 1Ignition coil cyl 1Ion sense module
What each part of P2891 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 8 | Area: transmission. |
| 91 | The exact fault in that area. |
What to do next
- Note P2891 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2891
What does P2891 mean?
P2891 means "Cylinder 1 Ion Current Sense Circuit Range/Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P2891?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P2891 fail an emissions test?
Yes, it can. P2891 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2891 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P2891 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.