P28B7 code meaning
Cylinder 10 Ion Current Sense Circuit High
Powertrain system Generic code P28xx codes Check engine light
What P28B7 means
P28B7 means the ion signal of cylinder 10 is stuck above its valid window. The usual suspects are a sense lead shorted to a supply or to a neighbouring ignition circuit, breakdown inside coil 10 that lets spark energy into the measuring path, and a poor ground at the evaluation side that shifts the reference upward. A falsely high signal could pass as continuous combustion or as permanent knock, so the engine computer typically discards it and retards timing on that cylinder for safety. Saab's later T8 module, which processes the ion signal of each coil on its own input pin, shows the cylinder-selective layout such a code assumes. No manufacturer documents P28B7 publicly. The low-side fault is P28B6, module supply problems are P28C0 to P28C2.
P28B7 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 P28B7
- MIL with high ion reading on cylinder 10
- Timing on cylinder 10 retarded for safety
- Misfire on cylinder 10 may be masked
Common causes of P28B7
- Most likelyCylinder 10 sense lead shorted to a supply or adjacent ignition circuit
- PossibleInternal breakdown in coil 10
- Less likelyPoor ground at the evaluation side
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 P28B7 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. |
| B7 | The exact fault in that area. |
What to do next
- Note P28B7 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 P28B7
What does P28B7 mean?
P28B7 means "Cylinder 10 Ion Current Sense Circuit High". P28B7 means the ion signal of cylinder 10 is stuck above its valid window. It is a generic code, so it means the same on every make.
Is it safe to drive with P28B7?
Drive gently and only to a workshop. With P28B7 the car can go into limp mode (reduced power) to protect itself.
Will P28B7 fail an emissions test?
Yes, it can. P28B7 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 P28B7 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 P28B7 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.