P289ACylinder 3 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
- P289A applies when the ion reading of cylinder 3 stays below the lower plausibility limit. Usually the signal path is pulled to ground somewhere, or the coil no longer supplies the measuring voltage of roughly 80 V that Saab's T7 cassette keeps across each gap between sparks. A cracked insulator or heavy carbon tracking on the plug can drain that voltage as well. Saab's own documentation shows why a dedicated code helps: on T7 four-cylinders a combustion signal shorted to ground produced no specific fault code at all, so synchronisation failed and only misfire codes appeared. With a stuck-low cylinder 3 signal, misfire and knock judgement for that cylinder is lost. The high-side fault is P289B.
- What you may notice
- MIL with low ion signal on cylinder 3
- Misfire codes or no misfire detection for cylinder 3
- Less power because timing is pulled back as a precaution
- Likely causes
- LikelyIon signal wire of cylinder 3 chafed through to ground
- PossibleCarbon tracking or cracked insulator on the cylinder 3 plug
- PossibleCoil 3 no longer builds up its measuring voltage
- 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 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.