P28A0Cylinder 5 Ion Current Sense Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL with ion fault stored for cylinder 5
- Misfire monitoring of cylinder 5 restricted
- Retarded timing and slightly reduced power
- Likely causes
- LikelyCoil of cylinder 5 with failed ion measuring circuit
- PossibleConnector or wire fault between coil 5 and the evaluation electronics
- RareEvaluation input for cylinder 5 defective
- 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: €60 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.