P3491Cylinder 12 Deactivation/Intake Valve Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- A ground fault on the control line of the cylinder 12 deactivation or intake valve actuator produces P3491. No manufacturer documents this code publicly; J2012 reserves the codes for cylinders 9 to 12 for engines with more than eight cylinders. The Aventador's cylinder deactivation system, introduced in 2012, shuts down one bank of six below 135 km/h, and Bentley's W12 drops one bank; neither publishes cylinder-level diagnostic codes. On GM V8s the corresponding low test watches for under 0.5 ohm to ground while the output is switched off, every 250 ms, and needs 20 hits in 25 samples. Because a grounded low-side line powers the actuator, the cylinder can be shut off against the module's will. P3489 (open) and P3492 (high) are the other circuit faults, P3495 the exhaust low.
- What you may notice
- Check engine lamp on
- Cylinder shut-off blocked
- Possible misfire on cylinder 12
- Likely causes
- LikelyCylinder 12 control wire shorted to ground
- PossibleInternal short in the cylinder 12 actuator
- RareWater ingress at the connector
- RareFaulty control module driver
- 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: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.