P28AB code meaning
Cylinder 7 Ion Current Sense Circuit High
Powertrain system Generic code P28xx codes Check engine light
What P28AB means
P28AB is set when the cylinder 7 ion signal sits above the highest value a healthy measuring circuit can deliver. Typical triggers are a signal lead touching a supply wire, moisture bridging the coil connector, or a coil whose ignition pulse bleeds into its measuring output. A constant high reading is treacherous for diagnosis because it can look like permanent combustion and so mask real misfire. Saab's T7 V6 shows comparable logic only per bank: its codes P1313 and P1324 flag a combustion line stuck above 5 V for 200 firings. No manufacturer publishes P28AB, and a V8 or larger engine using ion sensing is not publicly described. The low-side counterpart is P28AA; P28A9 handles readings that are in range but implausible.
P28AB 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 P28AB
- MIL lit with a high ion reading stored for cylinder 7
- Genuine misfire on cylinder 7 may go unreported
- Timing pulled back on cylinder 7, slightly less power
Common causes of P28AB
- Most likelyIon signal lead of cylinder 7 touching a supply wire
- PossibleMoisture bridging contacts in the coil 7 connector
- Less likelyCoil 7 leaking its ignition pulse into the measuring output
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 P28AB 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. |
| AB | The exact fault in that area. |
What to do next
- Note P28AB 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 P28AB
What does P28AB mean?
P28AB means "Cylinder 7 Ion Current Sense Circuit High". P28AB is set when the cylinder 7 ion signal sits above the highest value a healthy measuring circuit can deliver. It is a generic code, so it means the same on every make.
Is it safe to drive with P28AB?
Drive gently and only to a workshop. With P28AB the car can go into limp mode (reduced power) to protect itself.
Will P28AB fail an emissions test?
Yes, it can. P28AB 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 P28AB 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 P28AB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.