Powertrain, generic (extended)

P289C Cylinder 4 Ion Current Sense Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P289C stands for a general circuit fault in the ion measurement of cylinder 4, meaning no usable signal reaches the evaluation electronics from that plug. Cylinder 4 has a special role in Saab's Trionic four-cylinders: without a camshaft sensor, the engine fires cylinders 1 and 4 at the same time during start-up and decides from the ion response which of them is on the compression stroke. On the T8, coil 4 delivers its signal to processing module pin 15, and a combustion in cylinder 4 is passed on as a pulse to engine module pin 21(B). On a V6 with Saab's T7, cylinder 4 instead sits in bank 2 next to 2 and 6. Saab used in-house codes; no manufacturer publicly documents P289C.

Likely causes

Ion measuring stage in the coil of cylinder 4 failed
Open circuit between coil 4 and the processing module
Cylinder 4 input of the processing module defective

Symptoms

  • MIL with ion fault stored for cylinder 4
  • Extended cranking because cylinder 1 and 4 cannot be told apart reliably
  • Conservative ignition timing with reduced power

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 4ignition coil cyl 4ion sense module

Related codes

P289DP289EP289FP2890P2898P0304

References: law.cornell.edu, saabwisonline.com, saabwisonline.com.