Powertrain, generic (extended)

P28A7 Cylinder 6 Ion Current Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28A7 is logged when the ion signal of cylinder 6 is held above the upper limit the module accepts. A conductor in contact with battery voltage, crosstalk from the primary side of coil 6, or an evaluation stage driven into saturation are the typical electrical explanations. Saab's T7 V6 handled the comparable fault per bank: cylinder 6 belongs to bank 2, whose combustion line triggers Saab code P1324 when it stays above 5 V for 200 combustions; the knock information of that bank travels separately to engine module pin 62. A saturated channel leaves no room for the knock oscillations, so the module retards timing on cylinder 6. No manufacturer documents P28A7 publicly. The low-side counterpart is P28A6.

Likely causes

Ion conductor of cylinder 6 touching battery voltage
Crosstalk from the primary side of coil 6
Evaluation stage for cylinder 6 saturated

Symptoms

  • MIL with high ion signal on cylinder 6
  • Less power because of late ignition on cylinder 6
  • Knock on cylinder 6 may not be detected

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–650
Time0.3–2.5 h

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

Parts involved

spark plug cyl 6ignition coil cyl 6ion sense module

Related codes

P28A4P28A5P28A6P28A3

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