P28BCCylinder 12 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
- P28BC covers a wiring-level failure in the ion measuring path of cylinder 12 that keeps a valid signal from arriving, typically an open wire or a connector without contact. Cylinder 12 is the last one on a V12 or W12; no such engine with ion sensing is publicly known, and no manufacturer documents P28BC. On Saab's Trionic T8 each measuring channel needs two inputs at the detection module: the ion line from the coil and the ignition trigger of the same cylinder, which tells the module when to start listening. A break in either can leave the channel silent. With that, misfire counting and knock evaluation for cylinder 12 stop. The coil's primary circuit is a separate code, P0362. P28BD covers implausible signals, P28BE and P28BF the voltage levels.
- What you may notice
- MIL on with a circuit fault stored for cylinder 12
- No combustion feedback from cylinder 12
- Engine may run with reduced ignition advance
- Likely causes
- LikelyOpen ion signal wire or connector at coil 12
- PossibleIgnition trigger for cylinder 12 not reaching the detection module
- PossibleMeasuring stage of coil 12 dead
- RareCylinder 12 channel of the evaluation module faulty
- 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: €50 – €750
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.