P28A5 Cylinder 6 Ion Current Sense Circuit Range/Performance

P28A5 points to a cylinder 6 ion signal that exists but makes no sense for the operating point: too little combustion response, a trace that jumps between cycles, or one that departs from the remaining cylinders. Since ionisation follows the actual burn, a misfiring or lean cylinder 6 can trigger it as readily as a worn plug or a wet plug well. On Saab's T7 V6 the bank 2 module evaluates the ion flow of cylinders 2, 4 and 6 for knock, sending the result to engine module pin 62, and missing combustion signals on cylinder 6 feed misfire code P0306. If the signal is unreliable, knock control tends to retard timing more often. No manufacturer publicly documents P28A5; P28A4, P28A6 and P28A7 are the electrical siblings.

Likely causes

Symptoms

• MIL, often together with P0306
• Rough running at idle or light throttle
• Hesitation under acceleration

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.