Powertrain, generic (extended)

P28A0 Cylinder 5 Ion Current Sense Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28A0 reports that the ion current circuit of cylinder 5 delivers no evaluable signal. A cylinder 5 exists only on engines with five or more cylinders, which narrows the field considerably. The V6 of the Saab 9-5 with Trionic T7 is a documented ion-sensing example: cylinder 5 sits in bank 1 with 1 and 3, is triggered from engine module pin 31, and is fired together with cylinder 2 until synchronisation. That design, however, measures one combined voltage drop per bank, so a single-cylinder circuit fault cannot be isolated electrically; Saab instead counts missing combustion signals per cylinder for misfire code P0305. No manufacturer publicly documents P28A0.

Likely causes

Coil of cylinder 5 with failed ion measuring circuit
Connector or wire fault between coil 5 and the evaluation electronics
Evaluation input for cylinder 5 defective

Symptoms

  • MIL with ion fault stored for cylinder 5
  • Misfire monitoring of cylinder 5 restricted
  • Retarded timing and slightly reduced power

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–650
Time0.3–2.5 h

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

Parts involved

spark plug cyl 5ignition coil cyl 5ion sense module

Related codes

P28A1P28A2P28A3P28A4P0305

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