P28BC code meaning
Cylinder 12 Ion Current Sense Circuit
Powertrain system Generic code P28xx codes Check engine light
What P28BC means
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.
P28BC at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P28BC
- MIL on with a circuit fault stored for cylinder 12
- No combustion feedback from cylinder 12
- Engine may run with reduced ignition advance
Common causes of P28BC
- Most 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
- Less likelyCylinder 12 channel of the evaluation module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 12Ignition coil cyl 12Ion sense module
What each part of P28BC means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 8 | Area: transmission. |
| BC | The exact fault in that area. |
What to do next
- Note P28BC and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P28BC
What does P28BC mean?
P28BC means "Cylinder 12 Ion Current Sense Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P28BC?
Drive gently and only to a workshop. With P28BC the car can go into limp mode (reduced power) to protect itself.
Will P28BC fail an emissions test?
Yes, it can. P28BC is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P28BC to fix?
Difficulty: medium. A typical repair takes 0.5 to 3.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P28BC clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.