P28BECylinder 12 Ion Current Sense Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28BE is set when the ion reading of cylinder 12 stays below its minimum. On Saab's Trionic T8 each coil generates its own measuring voltage of about 120 V and keeps it applied to the plug; the module then reads how much current the ionised gas lets through. When that voltage is never built up – coil 12 has lost its bias stage – or leaks away through a cracked insulator, a soaked plug well or a sense lead grounded on a bracket, the evaluator sees a near-zero signal on every cycle. The engine computer then cannot confirm combustion in cylinder 12 and may report P0312 although the cylinder fires. No manufacturer documents P28BE, and twelve-cylinder engines with ion sensing are not publicly described. P28BF is the high-side counterpart, P28BC the open circuit.
- What you may notice
- MIL on with a low ion signal stored for cylinder 12
- Misfire code P0312 without noticeable roughness
- Fault often appears after washing the engine or in wet weather
- Likely causes
- LikelyWater or oil in the cylinder 12 plug well draining the measuring voltage
- PossibleCracked plug insulator on cylinder 12
- PossibleSense lead of cylinder 12 grounded against a bracket or the engine
- RareCoil 12 no longer builds up its measuring voltage
- 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: €30 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.