P28A5 code meaning
Cylinder 6 Ion Current Sense Circuit Range/Performance
Powertrain system Generic code P28xx codes Check engine light
What P28A5 means
P28A5 points to a cylinder 6 ion signal that exists but makes no sense for the operating point: too little combustion response, a trace that jumps between cycles, or one that departs from the remaining cylinders. Since ionisation follows the actual burn, a misfiring or lean cylinder 6 can trigger it as readily as a worn plug or a wet plug well. On Saab's T7 V6 the bank 2 module evaluates the ion flow of cylinders 2, 4 and 6 for knock, sending the result to engine module pin 62, and missing combustion signals on cylinder 6 feed misfire code P0306. If the signal is unreliable, knock control tends to retard timing more often. No manufacturer publicly documents P28A5; P28A4, P28A6 and P28A7 are the electrical siblings.
P28A5 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P28A5
- MIL, often together with P0306
- Rough running at idle or light throttle
- Hesitation under acceleration
Common causes of P28A5
- Most likelySpark plug of cylinder 6 worn or sooted
- PossibleWater or oil in the plug well of cylinder 6
- PossiblePoor combustion in cylinder 6 (injector, valve, compression)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 6Ignition coil cyl 6Ion sense module
What each part of P28A5 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. |
| A5 | The exact fault in that area. |
What to do next
- Note P28A5 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 P28A5
What does P28A5 mean?
P28A5 means "Cylinder 6 Ion Current Sense Circuit Range/Performance". P28A5 points to a cylinder 6 ion signal that exists but makes no sense for the operating point: too little combustion response, a trace that jumps between cycles, or one that departs from the remaining cylinders. It is a generic code, so it means the same on every make.
Is it safe to drive with P28A5?
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 P28A5 fail an emissions test?
Yes, it can. P28A5 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 P28A5 to fix?
Difficulty: easy. A typical repair takes 0.3 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P28A5 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.