P2890Cylinder 1 Ion Current Sense Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Some engines use the spark plug as a combustion sensor: between sparks a measuring voltage is applied, and the hot, ionised gas lets a small current flow whose shape reveals misfire and knock. P2890 is the basic circuit fault for this measurement on cylinder 1 – the module receives no usable ion signal from that cylinder at all. Saab built the principle into its Trionic engines: on the four-cylinder T8 the coil of cylinder 1 feeds its ion signal to a separate processing module, which also decides whether cylinder 1 or 4 is on the firing stroke, because the engine has no camshaft sensor. A dead cylinder 1 signal can therefore disturb synchronisation as well. Saab used its own codes; no manufacturer publicly documents P2890.
- What you may notice
- MIL with reduced knock and misfire monitoring on cylinder 1
- Longer cranking if cylinder identification is affected
- Retarded ignition and less power as a precaution
- Likely causes
- LikelyIgnition coil of cylinder 1 with failed ion measuring stage
- PossibleOpen ion signal wire or connector between coil 1 and the processing module
- RareFaulty ion processing module or engine control module input
- 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: €60 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.