P28A2Cylinder 5 Ion Current Sense Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28A2 is stored when the cylinder 5 ion reading stays under its lower threshold. The measurement relies on a constant bias across the plug gap between sparks – about 80 V on Saab's T7 discharge modules – and anything that drains it to ground pulls the reading down: a chafed signal conductor, a cracked plug insulator, or a coil whose bias supply has failed. On Saab's four-cylinder T7, a combustion line shorted to ground produced no dedicated fault code and surfaced only as misfire codes, which illustrates the gap such a low-side code closes. On Saab's V6 the bank 1 module serves cylinders 1, 3 and 5 together. No manufacturer publicly documents P28A2. P28A3 is the high-side fault.
- What you may notice
- MIL with low ion signal on cylinder 5
- Misfire codes for cylinder 5 may appear
- Safety ignition map reduces power
- Likely causes
- LikelySignal conductor of cylinder 5 chafed against ground
- PossibleCracked insulator on the cylinder 5 spark plug
- PossibleBias supply of coil 5 failed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €550
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.