Powertrain, shared range

P3491 Cylinder 12 Deactivation/Intake Valve Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Cylinder 12 control wire shorted to ground
Internal short in the cylinder 12 actuator
Water ingress at the connector
Faulty control module driver

Symptoms

  • Check engine lamp on
  • Cylinder shut-off blocked
  • Possible misfire on cylinder 12

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–900
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cylinder deactivation solenoidwiring harnessecm

Related codes

P3489P3490P3492P3495P0312P3400

References: law.cornell.edu, newatlas.com, gsi.ext.gm.com, bentleymedia.com.