Powertrain, generic (extended)

P289A Cylinder 3 Ion Current Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P289A applies when the ion reading of cylinder 3 stays below the lower plausibility limit. Usually the signal path is pulled to ground somewhere, or the coil no longer supplies the measuring voltage of roughly 80 V that Saab's T7 cassette keeps across each gap between sparks. A cracked insulator or heavy carbon tracking on the plug can drain that voltage as well. Saab's own documentation shows why a dedicated code helps: on T7 four-cylinders a combustion signal shorted to ground produced no specific fault code at all, so synchronisation failed and only misfire codes appeared. With a stuck-low cylinder 3 signal, misfire and knock judgement for that cylinder is lost. The high-side fault is P289B.

Likely causes

Ion signal wire of cylinder 3 chafed through to ground
Carbon tracking or cracked insulator on the cylinder 3 plug
Coil 3 no longer builds up its measuring voltage

Symptoms

  • MIL with low ion signal on cylinder 3
  • Misfire codes or no misfire detection for cylinder 3
  • Less power because timing is pulled back as a precaution

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–500
Time0.3–2 h

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

Parts involved

spark plug cyl 3ignition coil cyl 3ion sense module

Related codes

P2898P2899P289BP2896P289E

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