P28B8 code meaning
Cylinder 11 Ion Current Sense Circuit
Powertrain system Generic code P28xx codes Check engine light
What P28B8 means
P28B8 is the general circuit code for ion sensing on cylinder 11: the evaluation electronics receive nothing usable from that cylinder, most often because the line from coil 11 is broken or its connector has lost contact. Eleven cylinders only occur on V12 and W12 engines, and none of them with ion sensing is publicly described; no manufacturer documents P28B8. The layout such a code presumes exists on Saab's Trionic T8, whose detection module has a dedicated ion input for every coil. Losing it leaves the engine computer blind to misfire and knock on that cylinder, and on T8, which has no camshaft sensor, ion pulses also serve to find the firing order. P0361 concerns the primary side of coil K, not the measuring path; P28B9 to P28BB cover the range and level faults.
P28B8 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 P28B8
- MIL on with a circuit fault stored for cylinder 11
- Misfire and knock detection for cylinder 11 no longer available
- Cautious ignition timing with slightly reduced power
Common causes of P28B8
- Most likelyLoose, corroded or pushed-back pin in the cylinder 11 coil connector
- PossibleBroken ion signal wire between coil 11 and the evaluation module
- PossibleMeasuring stage inside coil 11 failed
- Less likelyCylinder 11 input of the evaluation module damaged
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 11Ignition coil cyl 11Ion sense module
What each part of P28B8 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. |
| B8 | The exact fault in that area. |
What to do next
- Note P28B8 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 P28B8
What does P28B8 mean?
P28B8 means "Cylinder 11 Ion Current Sense Circuit". P28B8 is the general circuit code for ion sensing on cylinder 11: the evaluation electronics receive nothing usable from that cylinder, most often because the line from coil 11 is broken or its connector has lost contact. It is a generic code, so it means the same on every make.
Is it safe to drive with P28B8?
Drive gently and only to a workshop. With P28B8 the car can go into limp mode (reduced power) to protect itself.
Will P28B8 fail an emissions test?
Yes, it can. P28B8 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 P28B8 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 P28B8 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.