Powertrain, generic (extended)

P28B0 Cylinder 9 Ion Current Sense Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28B0 marks an electrical circuit fault, usually an interruption, in the ion current measurement of cylinder 9. A ninth cylinder appears only on engines with ten or more cylinders, such as V10, V12 or W12 designs. Ion sensing as a production technique is publicly associated with Saab and Mecel, who brought it into series cars with the Trionic systems on four- and six-cylinder engines; for engines of ten or more cylinders no public application exists, and no manufacturer documents P28B0. The working principle would be unchanged: a small voltage across the idle plug gap, a current only when the hot gas ionises, and an evaluation channel per coil. Without that channel cylinder 9 loses misfire and knock evaluation; checks start at coil 9 and its connector.

Likely causes

Coil 9 connector not latched or with spread terminals
Ion output of coil 9 without function
Interrupted ion line of cylinder 9 in the harness

Symptoms

  • MIL with ion circuit fault for cylinder 9
  • Misfire and knock evaluation of cylinder 9 suspended
  • Slight loss of power from retarded 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 9ignition coil cyl 9ion sense module

Related codes

P28B1P28B2P28B3P28ACP28B4P0309

References: law.cornell.edu, en.wikipedia.org, saabwisonline.com.