P28A3Cylinder 5 Ion Current Sense Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL with high ion signal on cylinder 5
- Ignition retarded on cylinder 5, less power
- Knock events may not be recognised
- Likely causes
- LikelySignal path of cylinder 5 in contact with a voltage source
- PossibleCoil 5 feeding ignition energy into its measuring output
- RareDisturbed ground reference of the evaluation circuit
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.