Cylinder 12 Deactivation/Intake Valve Control Circuit Low
Code P3491 indicates a low voltage condition in the cylinder deactivation or intake valve control circuit for cylinder 12. This system, often found in engines with Active Fuel Management (AFM) or Variable Valve Timing (VVT), uses solenoids or actuators to disable intake valves during light load to improve fuel economy. A low circuit voltage suggests a short to ground, open circuit, or faulty component, which can prevent proper valve operation and trigger the check engine light.
01. Most Common Causes
- Faulty cylinder deactivation solenoid for cylinder 12
- Short to ground or open in the wiring harness
- Corroded or damaged connector at the solenoid
- Engine control module (ECM) internal failure
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced fuel economy
- Engine misfire or rough idle
- Loss of power or hesitation
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect the wiring and connector for cylinder 12 deactivation solenoid for damage or corrosion.
Step 3: Measure voltage at the solenoid connector with key on; should be near battery voltage. If low, check for shorts or opens.
Step 4: Test the solenoid resistance; compare to specs (typically 10-30 ohms). Replace if out of range.
Step 5: If wiring and solenoid are good, suspect ECM issue; perform ECM pin-out tests or reprogram/replace as needed.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause engine misfire, reduced performance, and potential damage to the catalytic converter. Have it diagnosed promptly.
How much does it cost to fix?▼
Typical repair costs range from $50 to $150 for DIY solenoid replacement, or $200-$400 at a shop including labor and diagnostics.