P28B4 code meaning
Cylinder 10 Ion Current Sense Circuit
Powertrain system Generic code P28xx codes Check engine light
What P28B4 means
P28B4 is the basic circuit code for the ion current measurement of cylinder 10; typically the line from coil 10 to the evaluation module is interrupted or the coil's measuring stage is dead. Ten cylinders mean a V10 at minimum, where this is the last cylinder in the numbering, or a V12 or W12, where it is not. No production engine of that size with ion sensing is publicly described, and no manufacturer documents P28B4. Saab's systems illustrate the stakes: without the ion signal, misfire counting and cylinder-selective knock control lose their input, and the T7 V6 even cut fuel to every cylinder once a single discharge module lost its supply. Start at coil 10, plug and connector; P28B5, P28B6 and P28B7 are the range and level faults.
P28B4 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 P28B4
- MIL with ion circuit fault for cylinder 10
- Cylinder 10 excluded from misfire and knock evaluation
- Possible power reduction through protective timing
Common causes of P28B4
- Most likelyOpen line between coil 10 and the evaluation module
- PossibleMeasuring stage of coil 10 dead
- PossibleCorroded terminals at the coil 10 connector
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 P28B4 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. |
| B4 | The exact fault in that area. |
What to do next
- Note P28B4 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 P28B4
What does P28B4 mean?
P28B4 means "Cylinder 10 Ion Current Sense Circuit". P28B4 is the basic circuit code for the ion current measurement of cylinder 10; typically the line from coil 10 to the evaluation module is interrupted or the coil's measuring stage is dead. It is a generic code, so it means the same on every make.
Is it safe to drive with P28B4?
Drive gently and only to a workshop. With P28B4 the car can go into limp mode (reduced power) to protect itself.
Will P28B4 fail an emissions test?
Yes, it can. P28B4 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 P28B4 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 P28B4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.