Powertrain, generic (extended)

P28B6 Cylinder 10 Ion Current Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28B6 is set when the cylinder 10 ion reading is persistently too low. The measuring bias that should sit across the gap between sparks is missing or being drained: a coil 10 whose bias generator has failed, conductive deposits bridging the plug insulator, a wet boot, or a sense wire with insulation damage touching ground. Saab's T7 applied 80 V for this purpose, the later T8 about 120 V; either way, a short to ground collapses it. The engine computer then lacks combustion confirmation for cylinder 10, may log P0310 and usually falls back to cautious timing. No manufacturer documents P28B6 publicly, and no ion-sensing engine with ten or more cylinders is known. The high-side code is P28B7.

Likely causes

Conductive deposits bridging the cylinder 10 plug insulator
Cylinder 10 sense wire with damaged insulation touching ground
Bias generator of coil 10 failed
Wet plug boot on cylinder 10

Symptoms

  • MIL with low ion reading on cylinder 10
  • P0310 may be stored as well
  • Cautious ignition timing, less pulling power

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–600
Time0.3–3 h

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

Parts involved

spark plug cyl 10ignition coil cyl 10ion sense module

Related codes

P28B4P28B5P28B7P28B2P0310

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