Powertrain, generic (extended)

P2890 Cylinder 1 Ion Current Sense Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Ignition coil of cylinder 1 with failed ion measuring stage
Open ion signal wire or connector between coil 1 and the processing module
Faulty ion processing module or engine control module input

Symptoms

  • 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

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–600
Time0.3–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

spark plug cyl 1ignition coil cyl 1ion sense module

Related codes

P2891P2892P2893P2894P0301P0325

References: law.cornell.edu, saabwisonline.com, en.wikipedia.org.