P28A0 code meaning
Cylinder 5 Ion Current Sense Circuit
Powertrain system Generic code P28xx codes Check engine light
What P28A0 means
P28A0 reports that the ion current circuit of cylinder 5 delivers no evaluable signal. A cylinder 5 exists only on engines with five or more cylinders, which narrows the field considerably. The V6 of the Saab 9-5 with Trionic T7 is a documented ion-sensing example: cylinder 5 sits in bank 1 with 1 and 3, is triggered from engine module pin 31, and is fired together with cylinder 2 until synchronisation. That design, however, measures one combined voltage drop per bank, so a single-cylinder circuit fault cannot be isolated electrically; Saab instead counts missing combustion signals per cylinder for misfire code P0305. No manufacturer publicly documents P28A0.
P28A0 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.3 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P28A0
- MIL with ion fault stored for cylinder 5
- Misfire monitoring of cylinder 5 restricted
- Retarded timing and slightly reduced power
Common causes of P28A0
- Most likelyCoil of cylinder 5 with failed ion measuring circuit
- PossibleConnector or wire fault between coil 5 and the evaluation electronics
- Less likelyEvaluation input for cylinder 5 defective
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 5Ignition coil cyl 5Ion sense module
What each part of P28A0 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. |
| A0 | The exact fault in that area. |
What to do next
- Note P28A0 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 P28A0
What does P28A0 mean?
P28A0 means "Cylinder 5 Ion Current Sense Circuit". P28A0 reports that the ion current circuit of cylinder 5 delivers no evaluable signal. It is a generic code, so it means the same on every make.
Is it safe to drive with P28A0?
Drive gently and only to a workshop. With P28A0 the car can go into limp mode (reduced power) to protect itself.
Will P28A0 fail an emissions test?
Yes, it can. P28A0 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 P28A0 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P28A0 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.