P28B5 Cylinder 10 Ion Current Sense Circuit Range/Performance

P28B5 reports an ion signal from cylinder 10 that is electrically valid yet implausible: its amplitude or timing after the spark does not fit the load point or departs from the remaining cylinders. Because ionisation depends on how hot and dense the burning charge is, causes include an eroded electrode gap, oil-wetted plugs, mixture errors on cylinder 10 or a compression loss. Saab's T7 V6 evaluated the ion flow of each bank for knock and retarded the affected cylinder step by step, so an untrustworthy signal tends to show up as erratic timing. No manufacturer publicly documents P28B5, and an ion-sensing V10 or V12 is not described. P28B4, P28B6 and P28B7 are the electrical faults; P0310 may accompany it.

Likely causes

Symptoms

• MIL, sometimes together with P0310
• Erratic ignition timing on cylinder 10
• Hesitation when accelerating

Repair estimate

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

Parts involved

Related codes

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