P28B5 code meaning
Cylinder 10 Ion Current Sense Circuit Range/Performance
Powertrain system Generic code P28xx codes Check engine light
What P28B5 means
P28B5 reports an ion signal from cylinder 10 that is electrically valid yet implausible: its amplitude or timing after the spark does not fit the load point or departs from the remaining cylinders. Because ionisation depends on how hot and dense the burning charge is, causes include an eroded electrode gap, oil-wetted plugs, mixture errors on cylinder 10 or a compression loss. Saab's T7 V6 evaluated the ion flow of each bank for knock and retarded the affected cylinder step by step, so an untrustworthy signal tends to show up as erratic timing. No manufacturer publicly documents P28B5, and an ion-sensing V10 or V12 is not described. P28B4, P28B6 and P28B7 are the electrical faults; P0310 may accompany it.
P28B5 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P28B5
- MIL, sometimes together with P0310
- Erratic ignition timing on cylinder 10
- Hesitation when accelerating
Common causes of P28B5
- Most likelyEroded electrode gap on the cylinder 10 plug
- PossibleOil-wetted plug in cylinder 10
- PossibleMixture error on cylinder 10
- Less likelyCompression loss in cylinder 10
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 10Ignition coil cyl 10Ion sense module
What each part of P28B5 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. |
| B5 | The exact fault in that area. |
What to do next
- Note P28B5 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 P28B5
What does P28B5 mean?
P28B5 means "Cylinder 10 Ion Current Sense Circuit Range/Performance". P28B5 reports an ion signal from cylinder 10 that is electrically valid yet implausible: its amplitude or timing after the spark does not fit the load point or departs from the remaining cylinders. It is a generic code, so it means the same on every make.
Is it safe to drive with P28B5?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P28B5 fail an emissions test?
Yes, it can. P28B5 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 P28B5 to fix?
Difficulty: easy. A typical repair takes 0.3 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P28B5 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.