Powertrain, generic (extended)

P28BB Cylinder 11 Ion Current Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28BB is stored when the cylinder 11 ion signal remains above the highest value the measuring circuit can legitimately produce. Common reasons are a sense wire shorted to battery voltage or to another ignition circuit, an internal breakdown in coil 11 that couples spark energy into the measuring output, and a missing ground at the evaluator that lifts the whole reference. The nearest published logic is per bank on Saab's T7 V6: P1324 needs a combustion line above 5 V throughout 200 combustions and clears only after 300 clean ones; Saab handled it as a Type III fault without a warning lamp. A stuck-high reading looks like constant combustion and can hide genuine misfire. No manufacturer documents P28BB. Its low-side partner is P28BA; the module supply is checked by P28C0 to P28C2.

Likely causes

Ion signal wire of cylinder 11 shorted to battery voltage or another ignition circuit
Internal breakdown in coil 11 feeding spark energy into the signal
Poor ground of the evaluation module shifting the reference

Symptoms

  • Stored code for a high ion signal on cylinder 11, lamp behaviour depends on the maker
  • Real misfire on cylinder 11 may go undetected
  • Retarded timing on cylinder 11

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–700
Time0.3–3 h

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

Parts involved

spark plug cyl 11ignition coil cyl 11ion sense module

Related codes

P28B8P28B9P28BAP28BFP28C2P0311

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