P28AD code meaning
Cylinder 8 Ion Current Sense Circuit Range/Performance
Powertrain system Generic code P28xx codes Check engine light
What P28AD means
P28AD means the cylinder 8 ion signal is electrically intact but does not fit what the computer expects for the operating point, or it deviates clearly from the other cylinders. CARB treats such rationality checks as part of the monitoring of input components next to tests for wiring faults and for values outside the valid band. The current through the gap rises with pressure and temperature of the burning charge, so weak combustion from a worn plug, a partly blocked injector or poor compression in cylinder 8 lowers it, while oil deposits can distort it. On Saab's T8 the engine computer evaluates each cylinder only inside a crank-angle window after the spark. No manufacturer publicly documents P28AD. Circuit faults are P28AC, P28AE and P28AF; a confirmed misfire adds P0308.
P28AD at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P28AD
- MIL, often together with P0308
- Rough running under load
- Knock control intervenes more often on cylinder 8
Common causes of P28AD
- Most likelyWorn electrodes or wrong gap on the cylinder 8 plug
- PossiblePartly blocked injector on cylinder 8
- PossibleOil deposits on the cylinder 8 plug
- Less likelyLow compression in cylinder 8
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Spark plug cyl 8Ignition coil cyl 8Ion sense module
What each part of P28AD 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. |
| AD | The exact fault in that area. |
What to do next
- Note P28AD 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 P28AD
What does P28AD mean?
P28AD means "Cylinder 8 Ion Current Sense Circuit Range/Performance". P28AD means the cylinder 8 ion signal is electrically intact but does not fit what the computer expects for the operating point, or it deviates clearly from the other cylinders. It is a generic code, so it means the same on every make.
Is it safe to drive with P28AD?
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 P28AD fail an emissions test?
Yes, it can. P28AD 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 P28AD to fix?
Difficulty: easy. 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 P28AD 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.