P28BDCylinder 12 Ion Current Sense Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P28BD reports that cylinder 12 delivers an ion signal of acceptable voltage whose content is not credible – its strength, timing or shape after the spark does not match the operating point or the rest of the engine. Saab's later detection module illustrates why content matters: it splits each raw ion trace with filters, a band-pass for the ringing that indicates knock and a low-pass for the slower part that describes combustion quality. A distorted trace corrupts both outputs. Likely sources are an eroded or oily plug, mixture errors on cylinder 12, carbon in the chamber or reduced compression. CARB counts such plausibility checks as part of input monitoring. No manufacturer documents P28BD. Electrical faults are P28BC, P28BE and P28BF; a real misfire adds P0312.
- What you may notice
- MIL on after the fault repeats on a later trip
- Occasional roughness, sometimes with P0312
- Knock control on cylinder 12 reacts erratically
- Likely causes
- LikelyEroded or oil-wetted spark plug on cylinder 12
- PossibleMixture error on cylinder 12 (injector, intake leak at that port)
- RareCarbon build-up in the cylinder 12 combustion chamber
- RareReduced compression on cylinder 12
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.