P28BB code meaning
Cylinder 11 Ion Current Sense Circuit High
Powertrain system Generic code P28xx codes Check engine light
What P28BB means
P28BB is stored when the cylinder 11 ion signal remains above the highest value the measuring circuit can legitimately produce. Common reasons are a sense wire shorted to battery voltage or to another ignition circuit, an internal breakdown in coil 11 that couples spark energy into the measuring output, and a missing ground at the evaluator that lifts the whole reference. The nearest published logic is per bank on Saab's T7 V6: P1324 needs a combustion line above 5 V throughout 200 combustions and clears only after 300 clean ones; Saab handled it as a Type III fault without a warning lamp. A stuck-high reading looks like constant combustion and can hide genuine misfire. No manufacturer documents P28BB. Its low-side partner is P28BA; the module supply is checked by P28C0 to P28C2.
P28BB at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.3 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P28BB
- Stored code for a high ion signal on cylinder 11, lamp behaviour depends on the maker
- Real misfire on cylinder 11 may go undetected
- Retarded timing on cylinder 11
Common causes of P28BB
- Most likelyIon signal wire of cylinder 11 shorted to battery voltage or another ignition circuit
- PossibleInternal breakdown in coil 11 feeding spark energy into the signal
- Less likelyPoor ground of the evaluation module shifting the reference
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 P28BB 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. |
| BB | The exact fault in that area. |
What to do next
- Note P28BB 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 P28BB
What does P28BB mean?
P28BB means "Cylinder 11 Ion Current Sense Circuit High". P28BB is stored when the cylinder 11 ion signal remains above the highest value the measuring circuit can legitimately produce. It is a generic code, so it means the same on every make.
Is it safe to drive with P28BB?
Drive gently and only to a workshop. With P28BB the car can go into limp mode (reduced power) to protect itself.
Will P28BB fail an emissions test?
Yes, it can. P28BB 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 P28BB to fix?
Difficulty: medium. A typical repair takes 0.3 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P28BB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.