Powertrain, generic (extended)

P28B8 Cylinder 11 Ion Current Sense Circuit

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P28B8 is the general circuit code for ion sensing on cylinder 11: the evaluation electronics receive nothing usable from that cylinder, most often because the line from coil 11 is broken or its connector has lost contact. Eleven cylinders only occur on V12 and W12 engines, and none of them with ion sensing is publicly described; no manufacturer documents P28B8. The layout such a code presumes exists on Saab's Trionic T8, whose detection module has a dedicated ion input for every coil. Losing it leaves the engine computer blind to misfire and knock on that cylinder, and on T8, which has no camshaft sensor, ion pulses also serve to find the firing order. P0361 concerns the primary side of coil K, not the measuring path; P28B9 to P28BB cover the range and level faults.

Likely causes

Loose, corroded or pushed-back pin in the cylinder 11 coil connector

Broken ion signal wire between coil 11 and the evaluation module

Measuring stage inside coil 11 failed

Cylinder 11 input of the evaluation module damaged

Symptoms

MIL on with a circuit fault stored for cylinder 11
Misfire and knock detection for cylinder 11 no longer available
Cautious ignition timing with slightly reduced power

Repair estimate

DifficultyMediumDIY possible

Parts and labour€50–750

Time0.5–3.5 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

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