Powertrain, generic (extended)

P28B4 Cylinder 10 Ion Current Sense Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28B4 is the basic circuit code for the ion current measurement of cylinder 10; typically the line from coil 10 to the evaluation module is interrupted or the coil's measuring stage is dead. Ten cylinders mean a V10 at minimum, where this is the last cylinder in the numbering, or a V12 or W12, where it is not. No production engine of that size with ion sensing is publicly described, and no manufacturer documents P28B4. Saab's systems illustrate the stakes: without the ion signal, misfire counting and cylinder-selective knock control lose their input, and the T7 V6 even cut fuel to every cylinder once a single discharge module lost its supply. Start at coil 10, plug and connector; P28B5, P28B6 and P28B7 are the range and level faults.

Likely causes

Open line between coil 10 and the evaluation module
Measuring stage of coil 10 dead
Corroded terminals at the coil 10 connector

Symptoms

  • MIL with ion circuit fault for cylinder 10
  • Cylinder 10 excluded from misfire and knock evaluation
  • Possible power reduction through protective timing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–700
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

P28B5P28B6P28B7P28B0P28B8P0310

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