Powertrain, generic (extended)

P28A3 Cylinder 5 Ion Current Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28A3 indicates a cylinder 5 ion signal locked above its permitted ceiling. Contact between the signal path and a voltage source, a coil 5 that injects ignition energy into its output, or a disturbed ground reference can cause it. The closest documented logic comes from Saab's T7 V6, where cylinder 5 is served by the bank 1 discharge module: Saab code P1313 detects an open or short to B+ on that bank's combustion line once it exceeds 5 V for 200 combustions, requires the engine to be running with ignition synchronised, and needs 300 clean combustions for the OK report. Naming cylinder 5 directly would require one measuring circuit per cylinder; no manufacturer documents P28A3 publicly. The low reading is P28A2.

Likely causes

Signal path of cylinder 5 in contact with a voltage source
Coil 5 feeding ignition energy into its measuring output
Disturbed ground reference of the evaluation circuit

Symptoms

  • MIL with high ion signal on cylinder 5
  • Ignition retarded on cylinder 5, less power
  • Knock events may not be recognised

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 5ignition coil cyl 5ion sense module

Related codes

P28A0P28A1P28A2P28A7

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