Powertrain, generic (extended)

P28BA Cylinder 11 Ion Current Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28BA means the cylinder 11 ion reading has fallen below its lower limit. Between sparks a bias voltage sits across the electrodes – 80 V on Saab's T7 – and burning gas lets a current flow that pulls this voltage down in proportion to pressure and temperature. If a fault drains the bias to ground, the evaluator registers the same collapse permanently: a sense wire chafed through, a plug insulator coated with conductive deposits, or water in the boot. Saab's manual notes that a combustion signal shorted to ground produced no dedicated code there, only misfire codes, so a separate low-signal code is a later refinement. No manufacturer documents P28BA, and no ion-sensing twelve-cylinder engine is publicly known. P28BB is the high-side fault, P28B8 the open circuit.

Likely causes

Ion signal wire of cylinder 11 chafed and touching ground
Conductive deposits on the cylinder 11 plug insulator
Moisture or a carbon track in the cylinder 11 plug boot
Bias voltage generation in coil 11 failed

Symptoms

  • MIL on with a low ion signal stored for cylinder 11
  • Misfire code P0311 possible although the engine runs smoothly
  • Power slightly reduced by conservative timing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–650
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

P28B8P28B9P28BBP28BEP28B6P0311

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