Powertrain, generic (extended)

P28B3 Cylinder 9 Ion Current Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28B3 shows that the cylinder 9 ion signal is held above the range a working circuit produces. Shorts from the sense line to a powered conductor, a coil 9 leaking high-voltage energy into its measuring output, or water in the connector can push it there. The fault matters for emissions monitoring, because a signal that always reports strong combustion would let real misfire on cylinder 9 go unnoticed. As an analogue, Saab's V6 bank codes needed 300 clean combustions before reporting the circuit OK again, after a sustained over-voltage had set them. No manufacturer documents P28B3, and no ion-sensing engine with nine or more cylinders is publicly known. P28B2 is the low fault, P28B0 the open circuit.

Likely causes

Cylinder 9 sense line shorted to a powered conductor
Coil 9 leaking high-voltage energy into its measuring output
Water in the coil 9 connector

Symptoms

  • MIL with high ion reading on cylinder 9
  • Real misfire on cylinder 9 can go unnoticed
  • Timing on cylinder 9 retarded as a precaution

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–650
Time0.3–3 h

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

Parts involved

spark plug cyl 9ignition coil cyl 9ion sense module

Related codes

P28B0P28B1P28B2P28AFP28B7P0309

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