P28A8 code meaning
Cylinder 7 Ion Current Sense Circuit
Powertrain system Generic code P28xx codes Check engine light
What P28A8 means
P28A8 covers a basic circuit fault in the ion current measurement of cylinder 7, so the module obtains no evaluable signal from that plug. A cylinder 7 only exists on engines with eight or more cylinders, and Saab, the best-known user of ion sensing, applied it to four-cylinder and V6 engines; no maker publicly describes an eight-cylinder version. No manufacturer publicly documents P28A8. Its physical position depends on the maker's numbering, which differs between brands on V8 engines. The principle stays the same: a bias voltage across the plug gap lets the burning gas conduct a small current, and a lost signal blinds misfire and knock assessment for that cylinder. Diagnosis starts at coil 7, its connector and the spark plug.
P28A8 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 P28A8
- MIL with ion fault stored for cylinder 7
- Misfire and knock monitoring of cylinder 7 unavailable
- Some power loss from protective timing
Common causes of P28A8
- Most likelyCoil of cylinder 7 with defective ion measuring function
- PossibleBroken wire or loose connector in the cylinder 7 ion circuit
- Less likelyCylinder 7 input of the evaluation electronics faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 7Ignition coil cyl 7Ion sense module
What each part of P28A8 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. |
| A8 | The exact fault in that area. |
What to do next
- Note P28A8 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 P28A8
What does P28A8 mean?
P28A8 means "Cylinder 7 Ion Current Sense Circuit". P28A8 covers a basic circuit fault in the ion current measurement of cylinder 7, so the module obtains no evaluable signal from that plug. It is a generic code, so it means the same on every make.
Is it safe to drive with P28A8?
Drive gently and only to a workshop. With P28A8 the car can go into limp mode (reduced power) to protect itself.
Will P28A8 fail an emissions test?
Yes, it can. P28A8 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 P28A8 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 P28A8 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.