P28C2Ion Sense Module Supply Voltage High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28C2 is stored when the voltage feeding the ion sense module exceeds its upper limit. Since the module derives its measuring and, in cassette designs, its ignition voltages from this feed, an excessive input can raise the bias across the plugs, push signals toward the top of their range and stress the converter inside. The cause is rarely the module: a failing alternator regulator, a jump start from a 24 V source or a poor ground at the module that makes the measured difference look larger are more typical. Saab's published ignition diagnostics have no overvoltage check at all, only the loss-of-supply codes, so there is no maker analogue for this case; the code follows the CARB demand to check inputs for out-of-range values. No manufacturer documents P28C2. P28C0 and P28C1 are the open and low faults.
- What you may notice
- Stored overvoltage code, often together with P0563
- Flickering or unusually bright lamps, battery gassing
- Erratic misfire or knock reports on several cylinders
- Likely causes
- LikelyAlternator voltage regulator letting the system voltage rise too high
- PossibleJump start or charger with excessive voltage (e.g. 24 V)
- PossiblePoor module ground distorting the voltage reading
- RareFaulty voltage measurement inside the module
- 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: €0 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.